Bit

Wikipedia also has an article about Bit.

A bit is a single base-2 integer representing either the value 'ON' (1) or 'OFF' (0). In the Pokémon games, the simple concept of an ON and OFF value is useful for binary switches, for example, the Pokédex flags use bits in 19 seen and own bytes to mark whether a Pokémon was seen or owned (8*19=152, which is enough values for every Pokémon).

An ordered collection of bits (usually 8) is commonly known as a byte.