Learner's definition of SEX
1 [noncount] : the state of being male or female
The form asks for your name, age, and sex.
The couple didn't know what the sex of their baby would be.
How do you tell the sex of a hamster?
discrimination on the basis of sex
the female/male sex
a sex change (operation) [=an operation in which a man's body is changed to be like a woman's body or a woman's body is changed to be like a man's]
2 [count] : men or male animals as a group or women or female animals as a group
This movie will appeal to both sexes. [=will appeal to both men and women]
a battle of the sexes [=a battle between men and women]
Some feel men are the more aggressive sex.
a single-sex dormitory [=a dormitory where only women or men stay]
3 [noncount] : physical activity in which people touch each other's bodies, kiss each other, etc.: physical activity that is related to and often includes sexual intercourse
— often used before another noun
All he ever thinks about is sex.
Her mom talked to her about sex.
She doesn't like all the sex and violence in movies.
He had sex with his girlfriend.
He has a low sex drive. [=he does not have a strong desire to have sex]
a sex shop [=a store that sells items relating to sex]
She has an active sex life. [=she has sex often]