Mahram
Here's a group of opposite sex Close Relatives of a woman, each called a "Mahram" of that women in Islam:
Father, Husband, Son, Brother, Grandfather (and Greatgrandfathers), Father in Law (father of husband), Grandfather in Law (and 'Greatgrandfather in Law's), Uncle, Uncles of Mother and Father (and Uncles of their ancestors)
A group of "Mahram"s of a man can also be determined the same way as above.
People from the same sex are also considered Mahram.
People can also become Mahram because of breast feeding with special conditions (in that case they are called for example "Milky Brother and Sister", "Milky Father and Daughter", "Milky Mother and Son" or etc.).
