If someone kills his or her own mother, it's called matricide. You can find plenty of matricide in ancient Greek myths.
The suffix -cide is a clue that something murderous is going on with this word: it means "killer," from the Latin -cida, "cutter or slayer." You can find it in words like insecticide and pesticide too. The first part of matricide comes from the root mater, or "mother."