Foreplay is anything sexual you do before you have sex. It can be whatever you want it to be- flirting, kissing, dancing, touching and caressing are just some examples. People have different ideas about what counts as foreplay and what counts as sex- so, some people think oral sex is foreplay, and some people think oral sex is sex. The sexual touch involved doesn’t have to penetrative to count as sex for some. It’s different for different people- it’s a personal thing.
Some people think sex is the same thing as intercourse- that is, sex is only sex when somebody puts their penis inside somebody else’s vagina. But some people would disagree with that- maybe they don’t enjoy “penis in vagina sex”, or maybe they and their partner both have a penis, or both have a vagina.
Some people think sex is when you are intimate with your partner- that sex is when you have private, romantic time alone with your partner and you can kiss and cuddle and show affection to each other. But some people would disagree with that- maybe they don’t enjoy “romantic sex”, or maybe they prefer sexual relationships which are more like “friends with benefits” or “one-night stands”.
Some people think sex is communicating sexual thoughts and ideas- that sex doesn’t have to be physical, and that sex can involve things like talking about sex or sexting. But some people would disagree with that- maybe they don’t enjoy “non-physical sex”, or don’t feel satisfied unless they touch their partner.
There are lots and lots of different ways of thinking about sex. In a way, asking “what is sex?” is a bit like asking “what is happiness?” Just like for your baby cousin, watching Peppa Pig and eating mashed potato might be happiness, while for your best friend, going to salsa dancing lessons might be happiness, people have completely different ideas about what sex means, and which parts of sex are enjoyable.
If you have a partner and you have sex with each other or are thinking about having sex with each other, why not ask them what sex means to them? That way, you have a better idea of what they enjoy and of what their boundaries are.