21st Century Sex: A to Z of pleasure in bed; EXTRACTED from The Sex Book: Want to impress your mates by being a font of all knowledge on things sexual? Here's an A to Z of sex with loads of erotic description. It really is as easy as, er, ABC.

Byline: CLARE GOLDWIN

Arousal: Women can take up to 20 minutes of touching to become fully aroused. Try stroking the skin using a prop such as a paintbrush or satin cloth to awaken the senses. Once a woman is aroused, natural lubrication usually occurs within 10 to 30 seconds. The breasts swell in size, sometimes by up to 20 per cent.

Brain power: Sex is constantly on our minds. Psychologist Paul Cameron interviewed more than 4,000 people and found men under 25 think about sex once every two minutes and women under 25 think about it once every five minutes.

We can spend hours fantasising about sexual scenarios and the mind can be sexually active at any time or anywhere. It offers a sexual freedom that is not restricted by society or relationships.

Coolidge Effect: Men's desire for sexual variety was named 'the Coolidge effect' after the former US President, Calvin Coolidge. During a visit to a farm in 1976, the President and his wife were taken off on separate tours. When Mrs Coolidge passed the chicken pens, she allegedly asked if the rooster copulated more than once each day.

"Dozens of times", was the answer.

"Please tell that to the President," Mrs Coolidge requested.

When the President passed the same pens and was told about the rooster, he asked: "Same hen, every time?"

"Oh no, Mr President, a different one each time," came the answer. The President nodded slowly. "Tell that to Mrs Coolidge."

Desire: A woman's sexual desire peaks around the time of ovulation. This is because in evolutionary terms it is important to mate when conception is morelikely. Studies show that a peak in sexual desire occurs around day 14 of a regular cycle, though other studies indicate that a a second peak in desire occurs just before or after menstruation.

There are times in everyone's life when desire is reduced or disappears. If you are busy, anxious or unhappy, when the first flush of a relationship is over and during pregnancy or early parenthood. Problems arise when lack of desire is not mutual. A partner may feel rejected and look for intimacy elsewhere. Sometimes temporary lack of desire becomes permanent, simply because you're used to it. Sexual counselling or therapy may help.

Erogenous zones: Skin is both a protective shield and a sensory organ containing nerve endings that are sensitive to touch, pain, pressure and temperature. Nerve endings are unevenly distributed in the body which means that lips, nipples, hands, fingertips and genitalia are more receptive to touch than other areas of the body.

Fetish: The word fetish originates from the medieval Portuguese word "feitico", which refers to religious relics with magical properties.

Today, people are defined as fetishists when they become aroused by things that are not usual objects of desire. Common fetishes include shoes, feet, rubber and latex.

Research shows fetishism is more common in men.

G-spot: The Holy Grail of a woman's anatomy, it was named in the 1950s after physician Ernest Grafenberg. He noted that during orgasm a swollen spot 3cms into the vagina is involved in an expulsion of fluid similar to male ejaculation. Though many women are extremely sensitive in this area, doctors still can't explain the phenomenon and the G-spot largely remains a mystery.

G also stands for Gynonudomania: a compulsion to rip off other people's clothes.

How Often? Contrary to expectation British women get more sex than men. According to the most up-to-date survey, 76.2 per cent of heterosexual women had sex last month compared to 72.5 per cent of heterosexual men. One in 23 men has paid for sex in the past five years. That figure rises to one in 11 men in London. But it's bad news for married couples.

Sexual frequency falls by 50 per cent during the first year and continues to slide. On average, married people between 35 and 55 have sex less than seven times a month and, after 65, you are lucky to have sex at all.

Infertility:If you have been trying to become pregnant for a year, your doctor is likely to refer you and your partner to a fertility clinic for testing.

Depending on the results, a number of things can be done. A woman can take fertility drugs to boost the number of eggs she produces. If sperm are struggling to reach the eggs, the process can be assisted by inserting them directly into the uterus, by a process known as intra-uterine insemination. Sometimes eggs are fertilised outside the body and then implanted. This process, known as in-vitro fertilisation (IVF), usually involves hormonal treatment that encourages several eggs to mature and can result in two or more eggs implanting. IVF is also used when there is a high chance of passing a genetic disease to the foetus. Women who cannot produce fertile eggs and men who have poor-quality sperm can opt to use donated sperm and eggs for any of the above procedures.

Jealousy: Men often report feeling jealous of a new baby (who seems to be getting all their partner's attention) and it is difficult to make love to someone if you feel vulnerable or undervalued. Meanwhile, the new mum is also less likely to want sex because breastfeeding lowers oestrogen levels which can decrease libido.

Kissing: Bored with French kissing? Try some of these instead. Butterfly kiss: Fluttering your eyelashes against your partner's face.

Kissing games: Adults are rediscovering teenage games such as spin the bottle. Sit in a circle and take it in turns to spin a bottle in the centre. When the bottle settles, the spinner has to kiss the person it is pointing at.

Tasty kisses: Try salting your lips or dusting them in icing sugar or cocoa powder. Pass liquids or foods, such as champagne, ice cubes, strawberries, ice cream or lemon sherbet, from mouth to mouth

Deep tongue: Purse your lips in a firm O and suck your partner's tongue through your lips to the back of your throat (your whole mouth will almost be inside your partner's). Release the tongue and then suck it back in. It should be moved back and forth, as if simulating fellatio. Take turns at being the passive one.

Love: It is not known whether this is a chemical, psychological or imagined state, but the symptoms are very real.

Side effects include passion, obsession, generosity and happiness. In its early stages people often show loss of appetite and concentration. Latest research puts this down to the release of dopamine which floods the brain in passionate moments. This pleasure hormone also makes you lose sleep and feel detached from the real world.

Mmmmm, you smell nice: Research shows that vanilla is the most universally attractive smell and also the closest scent there is to breast milk. So the next time you want to pull, try wearing a few drops of vanilla essence.

It might be more effective than knocking them out with perfume. Sandalwood is another tried and tested aphrodisiac.

It's now known that it contains androstenone, a hormone produced by men and women which boosts the libido.

Nice hairdo: It's not just the hair on your head that can benefit from a makeover. But, beware, bleaching tends to turn pubic hair orange and can cause severe irritation on sensitive skin.

Black dye tends to look the most convincing, but use dye made for beards because it is better for stronger hair. The Hollywood wax is now a popular hairstyle for women, in which all the pubic hair is removed.

More moderate styles are "the arrow", in which hair is trimmed into a downward pointing shape and "the runway" or "Brazilian" in which just a narrow strip is left down the centre.

A new craze is the "Tiffany box". This involves shaving everything off bar a small square, which is then dyed a shade of duck-egg blue.

Orgies: Orgies have probably been around forever but they are usually referred to as "group sex" these days. Generally group sex events are organised through invites and adverts. Organisers of straight orgies often stipulate that each woman brings a male friend, or vice-versa, to ensure there is "plenty to go around". Usually the only rule is that you ask before joining in.

Priapism: A medical term for an erection that won't go down. It can be very painful and requires immediate treatment. Priapism occurs without sexual stimulation and may happen because of infection, a blood clotting defect or nerve damage. This stops blood from draining away from the penis.

Quality not quantity: When it comes to sex there is no such thing as "normal" and it doesn't always come naturally. Practise helps, confidence helps more. Sex itself is really very simple - there are only six sexual positions and everything else is a variation on each theme. The best thing to do is try a variety to see what works for you.

Role play: Many couples are turned on by sexy power games. Popular scenarios include doctor and patient, maid and employer, sex worker and client, teacher and student, priest or nun and sinner, even owner and dog. Essentially, the relationship has to be one in which one party might be manhandled or controlled by the other. Hire costumes for added reality but don't forget to dry clean them before they go back to the shop - it could be embarrassing.

Size matters? Don't get a complex about the monstrous members displayed in porn mags and movies. The truth is that porn stars are selected for size and photographed from below and closely shaved to make their appendages look bigger. According to the Kinsey Institute for Sex Research in the US, the average size of most men's erections is 15.25cm (six inches).

Ninety per cent of all penises are between 13 and 18cm (5.1 and 7.1 inches). The shortest functioning penis to have been recorded was 1.5cm (0.67inches) and the longest was 30cm (11.8in).

If you're not particularly well hung then look at your penis in the mirror, rather than looking down at it which doesn't allow you to see the full length. And if you're with a new partner then impress her by making sure the room is warm before getting your kit off.

If you're cold and unrelaxed then your balls will shrivel and there'll be less blood flow, making your package appear smaller. After a warm bath is ideal because your scrotum and testicles will hang down further away from your body, blood flow to the penis will increase and you'll look better endowed.

Testosterone: This hormone is the basis of our sex drive (libido). In both sexes, high levels of testosterone can increase sexual thoughts, fantasies and the desire to have sex. It can increase self-confidence and it has antidepressant qualities but too much promotes aggressive behaviour.

Male levels of testosterone fluctuate over a 24-hour period, rising during the night and reaching a peak in the early morning hours - which is why men often wake with an erection.

Unfair: Three quarters of men reach orgasm within two minutes of starting sexual intercourse, 75 per cent of men in partnerships always have an orgasm with their partner, but only 28.6 per cent of women do. Eighty per cent of women require clitoral stimulation to achieve full arousal and orgasm.

Voyeurism: Watching other people - usually undressing or having sex - in order to become sexually aroused. Voyeurs may go to sex parties to watch people or they may be more covert "peeping toms" - people who hide near homes and watch through windows. It is thought that erotic gratification is heightened by secrecy and risk. This can become a problem for people who become obsessed by watching and find themselves getting led away by the police.

Wife-swapping: Also known as swinging, this is when couples swap their partners for sex. Swingers sometimes use euphemisms to communicate with like-minded people. For example "likes English culture" means "likes spanking", "Likes Roman culture" means "likes orgies". "The door is always open" means couples will be expected to have sex in the same room.

Xenophilia: Being sexually aroused by strangers. Xenophiles are turned on by meeting new people but once they have managed to seduce them the thrill diminishes. They like to have sex with people of different ethnicities and nationalities. As a result they enjoy travel and meeting people. A lot.

Yes, yes, yes: A potted history of the female orgasm. Around 400 BC, Greek mathematician Hippocrates had a theory that conception occurred as a result of mixing male and female semen and that women required sexual pleasure to ensure theirs was plentiful. Unfortunately, Aristotle then suggested that only male semen was fertile and female pleasure went out of the window.

Through the Middle Ages, the Church and medical profession took the view that female sexuality was associated with the devil. In the 17th Century, female arousal was diagnosed as an illness. But by the 18th Century female orgasm had become a recognised phenomenon.

Zelophilia: A person who becomes aroused by jealousy. They thrive on the adrenaline that is produced by the body in response to anger or fear. They purposely set up sexual situations in which their partner will solicit sexual attention from rivals.

- EXTRACTED from The Sex Book (Cassell Illustrated, pounds 16.99) by Suzi Godson. Copyright Suzi Godson. To get 15 per cent off The Sex Book, call Mirror Direct on 0870 0703 200. Free P&P.