Celibacy: 1. abstention from sexual relations. 2. abstention by vow from marriage: the celibacy of priests. 3. the state of being unmarried.
Abstinence: The act or practice of refraining from indulging an appetite or desire, especially for alcoholic drink or sexual intercourse. -- c.1300, "forbearance in indulgence of the appetites" -- Specifically of sexual appetites from mid-14c.
In the case of Catholic priests and nuns, there is a prohibition of both marriage AND sexual relations. You're not suggesting that priests and nuns are free to engage in sexual relations, are you?
The Church does not differentiate between the clergy and the laity in its prohibition against sexual activity out of wedlock, but places no celibacy requirement on the laity.