المعنى الاصطلاحي :

Every sane, adult Muslim whom a man or woman is permanently forbidden from marrying due to a legitimate reason.

الشرح المختصر :

The "mahram" (permanently unmarriageable kin) of a woman is every person who is permanently prohibited from marrying her, and the reasons of permanent prohibition are three: 1. Blood relation, which is the connection between two people by common birth. They are the woman’s father, son, brother, nephew either from her sister or brother, paternal uncle, and maternal uncle. 2. Suckling relation, which means that the breast milk of a woman reached the stomach of a baby, under certain conditions, like a woman’s foster father. 3. Marriage relation, which takes place by means of matrimony, like the woman’s father-in-law and her stepson.

التعريف اللغوي المختصر :

"Mahram" has the same meaning of haram and "muharram": unlawful and forbidden. Opposite: halal. Original meaning of "tahreem": forbidding someone from doing something. The "mahram" is a person whom one is forbidden from marrying.