"Fornication" translated from the Greek word "porneia." Many later translations use the phrase "sexual immorality." Fornication is any sexual intercourse outside the male/female marriage bond.

porneia
Thayer Definition:
1) illicit sexual intercourse
1a) adultery, fornication, homosexuality, lesbianism, intercourse with animals etc.
1b) sexual intercourse with close relatives; Lev. 18
1c) sexual intercourse with a divorced man or woman; Mar_10:11-12
2) metaphorically the worship of idols
2a) of the defilement of idolatry, as incurred by eating the sacrifices offered to idols
Part of Speech: noun feminine

cf. Matthew 5:31-32; Matthew 19:3-12; Romans 1:17-2:16