Shit is a word considered vulgar and profane in Modern English. As a noun it refers to fecal matter, and as a verb it means to defecate; in the plural ("the shits") it means diarrhea. Shite is a common variant in British and Irish English.
From Old English scite (“dung”), scitte (“diarrhoea”), from Proto-Germanic *skīta-, *skītaz, from Proto-Indo-European *sḱeyd-, *skeyd- (“to split, divide, separate”). Related to Middle Saxon (Middle Low Saxon) schite, New Saxon (New Low Saxon) Schiet, Middle Dutch schitte (Dutch schijt)...