Fornication (Greek ‘porneia’) is voluntary sexual relations between two people who are not married to each other and are also not married to anyone else.
The word "fornication" is the Greek "porneia," πορνεία, and occurs in six places: Matthew 15:19; Mark 7:21; John 8:41; Acts 15:20, 29; 21:25. The term "sexual immorality" is the Greek word "pornos," πόρνος and occurs twice in 1 Cor. 6:9; Heb. 13:4.
The Bible speaks of spiritual fornication as worshiping any God besides the true and living God: Judges 2:17; Jer. 3:8; Rev. 14:8; 17:2; 18:3; 19:2
Adultery occurs when a married person voluntarily has sexual relations with another person who was not his or her spouse.
Rape is the involuntary force of sexual relations upon another person and against the will of that person.
See also Adultery.