The "rational" people over at RationalWiki have an article on Sex.
This is a disambiguation page.
Sex is a term denoting different things.
Biological Sex, ie. in the context of reproduction, the categorization of gametes (for example sperm and egg) into sexes, such as “male” and “female”.1)
Sexual Intercourse, or more commonly just “sex”, the process of at least two sexually reproductive organisms engaging in activities involving their sexual organs. Procreative or not.
Sexual Reproduction, the modus of procreation of sexually reproductive organisms.
1)
Not necessarily male and female. Isogamous organisms exist and their sexes do not fall into those categories, instead referred to as, for example, + and -.