Celibacy may refer either to being unmarried or to sexual abstinence. A vow of celibacy is a promise not to enter into marriage. Some writers prefer this usage of "celibacy", while others use it interchangeably as a synonym for abstinence.
The old meaning of this term was "to have sexual intercourse only with one's wife".
The term involuntary celibacy refers to lack of sexual intercourse for reasons other than (voluntary) abstinence, e.g. shyness / love-shyness.