What does the term mahram, which derives from the Arabic word haram (forbidden) refers to those persons with whom sex is forbidden, mean for Muslim women?

[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]

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.