Like zinā (fornication or adultery), liwāṭ was a penetrative act of the penis. As with zinā, any act that did not involve this penetration fell into a lower category of offense. Sex acts between women (ex., siḥāq) could thus not rise to the severity of liwāṭ. As in the case of heterosexual activity, other same-sex contact was condemned and could even be punished by a judge’s discretion. But nothing matched liwāṭ, “the greatest indecency (al-fāḥisha al-kubrā)” either in moral condemnation or in the severity of punishment.
From an article is published in the American Journal of Islamic Social Sciences 34, no. 3 (2017) page 4, by Jonathan Brown. Source