Sex is the attribute of being either male or female, categories which reflect biological reproductive functions. The female sex is defined as the one which produces the larger gamete (the egg) and which typically bears the offspring. In contrast, the male sex has a smaller gamete (sperm) and rarely bears offspring.
Sex can also refer to sexual intercourse, the physical act of reproduction, also known as "sexual relations" or "having sex."
In some animals, sex may be assigned to specific structures rather than the entire organism. Earthworms, for example, are normally hermaphrodites.
For a more detailed treatment, see Gender roles.
"Sex" defines what is biologically present, whereas "gender" defines what society expects of persons of different sexes. The distinction is important in law, as it tends to forbid discrimination on the basis of either, e.g. effeminate men cannot be fired for not acting according to their "gender". In other areas the distinction is primarily important for more abstracted social and legal arguments, rather than everyday use.
The term sex is often used to denote the activity of sexual relations, and as such it is subject to laws of social conduct.
Sexual morality in the Bible
According to the Bible, if you're gay, you're worth nothing
- Grammar for a discussion of grammatical gender