A bit is an information unit used in computing and information theory. It is the smallest unit of storage currently used in these fields, although much research is going on in quantum computing with qubits. A single bit (short for binary digit) is a 0 or a 1, or a true or a false, or for that matter any two mutually exclusive states. A byte is a collection of bits, originally variable in size but now usually eight bits. Eight-bit bytes are also known as octets. There are also terms for multiple bits using the standard range of prefixes, eg. kilobit (kb), megabit (Mb) and gigabit (Gb).

By extension, ones or zeros in a computerised binary number (or a byte) are called bits.

Telecommunications or computer network traffic volume is usually described in terms of bits per second. For example, a "56 kbps modem" is capable of transferring data at 56 kilobits, kb, in a single second (which is equal to 7 kilobytes, 7 kB, with capitalised B to mark that we are talking about bytes and not about bits; in case of doubt, b is considered to mean bit); Ethernet transfers data at speeds ranging from 10 megabits per second to 1000 megabits per second (from 1.25 to 125 megabytes per second). The SI prefixes kilo-, mega-, etc., are sometimes modified in meaning when applied to bits and bytes: for an explanation, see Binary prefixes.

For more information see integral data type.

See also: Bitstream, Information entropy, Qubit

A bit is a piece of metal placed in a horse's mouth and connected to reins to direct the animal.
A bit, also called a drill bit is fitted to a rotary drill and is used to drill holes.