Sanitary towels are cotton/material pads that fit into someone's underwear (knickers) when they are having a period. The towels soak up blood, but need to be changed every few hours. This depends on if you have a heavy period or not.

The pouch on the body next to the penis that contains the testicles.

A fluid that contains a mixture of secretions from  male reproductive glands and sperm cells. Semen comes out from the penis when someone ejaculates.

Sexting is when someone shares sexual, naked or semi-naked images or videos of themselves or others, or sends sexually explicit messages. They can be sent using mobiles, tablets, smartphones, laptops – any device that allows you to share media and messages. This is illegal if you are under 18; see our Sexting page for more information.

Having sex or doing things of a sexual nature with another person (like fingering or oral sex).

Also known as getting turned on or being horny. Something happens to make you feel in the mood for sex, you could be alone or with a partner when this occurs. This can include having an erection if you have a penis, or the vagina becoming wetter.

When someone touches another person sexually without their consent. This can include groping, forced kissing, or any kind of unwanted sexual contact.

A nationwide network of clinics where you can go for free and confidential advice about sex and contraception. These also provide services specifically for young people under 25. Click here to find one near you.

Sexual contact between two people, usually involving someone inserting an erect penis into a vagina. However, sexual intercourse can also refer to any type of sexual contact between two people.

A person’s emotional, romantic and/or sexual attraction to another person.

Infections that are passed on in sexual activity. There are up to 25 STIs, some of which are more common and dangerous than others. The best way to protect against them is to always use a condom. See our STI page for more information.

This is when people may be having a sexual relationship without long term commitment.

When people give each other oral sex at the same time, with their genitals facing the other person's face.

A smear test (cervical screening) is a test to prevent cancer, by checking the health of your cervix. Cells are taken from women or people with a cervix using a speculum (a small metal or plastic instrument), which goes inside the vagina. The test isn't painful, but it might be a little uncomfortable. If you have a cervix you should have a test every three years from 25 to 50, and then every 5 years until you are 64 years old and will be invited by a letter from the NHS. Integrate into cervical screening.

Sperm are male reproductive cells that make up semen, which is produced when someone with a penis ejaculates. Sperm is produced in the testes.

Spiking is giving someone alcohol or drugs without them knowing or agreeing. For example, in their drink or with a needle. Spiking can happen to anyone anywhere – no matter their age, gender, sexuality or ethnicity. It can be carried out by strangers or by people you know.

When people are cuddling in bed, with one person behind the other, facing in.

When someone bleeds outside of their period, sometimes this can be more common if someone is on a contraceptive pill. If someone bleeds after sex, or outside of their period they should seek medical help from the GP.

When someone has an operation to prevent pregnancy or getting a partner pregnant.

You should  test for STIs if you have had unprotected sex without a condom, and/or if you have new partners. To test for chlamydia or gonorrhoea, if you have a vagina you need to do an internal swab, and if you have a penis you need a urine sample. To test for HIV and syphilis you need to do what is known as the 'finger prick' test. This takes a small sample of blood and tests for infections. It is important to test for STIs even if you do not have any symptoms.

Another word for heterosexual.

A small piece of material or cotton that is used to take a sample of body fluid.

A sexually transmitted infection, which may go unnoticed and can spread without either partner knowing. It is passed during sex or sexual activity and can be serious if left untreated.