Binary digIT = bit

One mathematical bit can define two levels or states, on or off, black or white, 0 or 1 etc.; – two bits can define four levels, three bits eight, and so on: generally 2n, where n = the number of bits. In image terms 10 bits can define 1024 levels of brightness from black to white (with ITU-R BT.601 and 709, 64 = black and 940 = white).