What is the definition of "adulteress" (al-zāniyah) in the noble verse: "The adulterer shall not marry except an adulteress or an idolatress; and forbidden is that unto the believers"? And does this description apply to someone who committed the act once or twice, whether willingly or unwillingly?

A woman who commits adultery by choice is considered an adulteress. However, if she is forced, she is not considered an adulteress, and no legal punishment (hadd) is imposed on her. It is permissible to marry an adulteress if she repents and her womb is cleared (of pregnancy), based on the Almighty's saying: ﴿The adulterer does not marry except an adulteress or a polytheist, and as for the adulteress, none marries her except an adulterer or a polytheist, and that has been forbidden to the believers﴾ [An-Nur: 3], and the Prophet's (peace be upon him) saying: «A pregnant woman should not be impregnated until she gives birth, and a non-pregnant woman until she has had one menstrual period.»