Sex to me is a genital and sensual pleasure human beings get from having intimate physical contact with themselves.

A lot of people usually think that there must be intercourse before it is can sex. But even foreplays too can be called sex because people get sexual pleasure from it too.

Even masturbation, no matter how it is frowned at, can be called sex because there is a sexual gratification and discharge those who masturbate get from masturbating. So I will say that sex can be between two people or one person.