sexual intercourse between people not married to each other.
What does the word of God say about it?
1 Thessalonians 4:3
For this is the will of God, even your sanctification, that ye should abstain from fornication:
1 Corinthians 6:18
Flee fornication. Every sin that a man doeth is without the body; but he that committeth fornication sinneth against his own body.
But fornication, and all uncleanness, or covetousness, let it not be once named among you, as becometh saints;
1 Corinthians 6:13
Meats for the belly, and the belly for meats: but God shall destroy both it and them. Now the body is not for fornication, but for the Lord; and the Lord for the body.
1 Corinthians 7:2
Nevertheless, to avoid fornication, let every man have his own wife, and let every woman have her own husband.
1 Corinthians 10:8
Neither let us commit fornication, as some of them committed, and fell in one day three and twenty thousand.
Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness,
Mortify therefore your members which are upon the earth; fornication, uncleanness, inordinate affection, evil concupiscence, and covetousness, which is idolatry:
1 Corinthians 5:1
It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles, that one should have his father’s wife.
2 Corinthians 12:21
And lest, when I come again, my God will humble me among you, and that I shall bewail many which have sinned already, and have not repented of the uncleanness and fornication and lasciviousness which they have committed.