Asalamualaykumwarahmatullahiwabarakatahu can you explain to me the thing called "thighing" also pronounced "mufa

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

The term Mufaakhathah means to have foreplay with the wife in between her thighs. It is reported in one narration that when the Prophet wanted to enjoy one of his wives who was in menstruation, he would put a piece of cloth on her vagina (i.e. cover it). [Ibn Maajah].

The author of Faydh Al-Qadeer interpreted the expression 'if he wanted to enjoy to mean having all permissible foreplay but avoiding the vagina [or the anus], like in between her thighs (i.e. Mufaakhathah).   

Allaah Knows best.