Mahram simply means someone's relative women that he cant get married too like his kids, wife's sister, his aunts, his mother or mother-in-law, his grand mother.

[edit] Who is mahram? Anyone whom a Muslim is not allowed to marry is mahram, if they are of the opposite sex and have reached puberty. A partial list of what is considered a "mahram" can be found in Surah 24, Ayah 31, of the Quran. A woman's opposite-sex mahrams fall into four categories (three categories in the strict-sense definition that does not count one's spouse). Note that mahrams for a man can be derived in a similar manner. permanent or blood mahrams with whom one is mahram by a blood relationship: father, grandfather, great-grandfather and so on; brother; son, grandson, great-grandson; uncle, parents' uncle, grandparents' uncle and so on; nephew, grandnephew, great-grandnephew and so on; in-law mahrams with whom one becomes mahram by marrying someone: father-in-law; son-in-law; stepfather (mother's husband) if their marriage is consummated; stepson (husband's son) if her marriage is consummated; rada or milk-suckling mahrams with whom you become mahram because of being nursed by a woman. When a woman acts as a wetnurse (that is, she breast feeds an infant that is not her own child) for a certain amount of time under certain conditions, she becomes the child's rada mother and all said about blood mahrams applies here, like rada father/mother, rada sister/brother, rada aunt/uncle and so on. In English these can be referred to as milk brother, milk-mother, etc. (See also breastfeeding fatwa.) All non-Muslim Males as mahrams: All non-Muslim men are "mahram" (forbidden) for a Muslim woman to marry. The Quran specifically forbids a Muslim woman from marrying any non-Muslim man, which is today still recognized as applicable both by Muslim and non-Muslim experts alike.[1]