Zina according to the Quran is sexual intercourse outside marriage between consenting adults, whether they are married or not.
The Arabic word Zina refers to both adultery as well as fornication and there is no distinction between married or unmarried persons.
THE ROOT WORD FOR ZINA IS ZAY-NUN-YA
Zay-Nun-Ya = to mount, the mounting upon a thing, to commit fornication/adultery, fornicator/adulterer.
Yaznuuna (imp. 3rd p.m. plu): They commit adultery or fornication
Yazniina (imp. 3rd p.f. plu.): They commit adultery or fornication
Zaanii (act. pic. m. sing it is Zaaniin where final nuun is dropped): One who commits adultery or fornication; Adulterer or fornicator.
Zaaniyatun ( act. pic. f. sing.): Adulteressor or fornicatoress
zana vb. (I)
yazni impf. act. 25:68, 60:12
zina n. vb. 17:32
ZINA IS ONE OF THE FORBIDDEN DEEDS, ONE OF THE SERIOUS SIN MENTIONED AFTER SHIRK AND KILLING
25:68 And those who do not call on any other god with God; nor do they take the life which God has made forbidden, except in justice; nor do they commit adultery. And whoever does will receive the punishment.
PUNISHMENT FOR ZINA
24:2 The adulteress (Zaniatu) and the adulterer (Zani), you shall lash each of them with one hundred lashes, and do not let any pity overtake you regarding the system of God if you believe in God and the Last Day. And let a group of the believers witness their punishment.
QURAN SPEAKS OF MARITAL RELATIONS BETWEEN ADULTERERS AND ADULTERESSES
24:3 The adulterer (Zani) will only marry an adulteress (Zaniatu) or she who is a polytheist. And the adulteress (Zaniatu) , she will only be married to an adulterer (Zani) or he who is a polytheist. And such has been made forbidden for the believers.
The Qur’an forbids believers from entering into a marital relationship with those guilty of Zina. The guilty parties are allowed to marry each other and live. This clearly proves that Zina is a sinful act.
ZINA HAS BEEN DESCRIBED AS IMMORAL AND AN EVIL PATH
17:32 And do not come near ADULTERY (ZINA), for it is immoral (Fahishatin) and an evil path.
ZINA IS PROHIBITED FOR BELIEVING FEMALES
60:12 O prophet, if the believing females come to make allegiance to you that they will not set up anything besides God, nor steal, nor commit ADULTERY (ZINA), nor kill their children, nor fabricate any falsehood, nor disobey you in any matter which is righteous, then you shall accept their allegiance, and ask God to forgive them. God is Forgiver, Merciful.