To go without sex, either willingly or not. Reasons include personal, religious, social, or bad luck. Only cure for a celibate individual is a slut or large amounts of alcohol to make the celibate person forget the aforementioned reasons.
Joe was scared of hell, so he decided to remain celibate.
Brian was fat, therefore he was forced to be celibate and instead frequently jerked off.
Due to Anne's many STD's, she laid off the pipe and went celibate.