Meaning of “sex” - Learner’s Dictionary

sex

noun uk us /seks/
ACTIVITY [ U ]

B1 sexual activity between people:

to have sex with someone
sex education
MALE OR FEMALE [ U ]

B1 the fact of being male or female:

Do you know what sex the baby is?
the female/male/opposite, etc sex

people who are female/male/the other sex from you, etc

(Definition of “sex” from the Cambridge Learner’s Dictionary © Cambridge University Press)