Bit
A bit is a binary digit with one of two possible values, conventionally written as 0 or 1.
Definition
A bit, short for binary digit, is a unit with two possible values, conventionally 0 and 1. Physical systems may realize those values with voltage levels, magnetic states, light, or other distinguishable conditions.
A bit describes a binary choice, not what the choice means. Its interpretation comes from a surrounding number, character encoding, file format, instruction, or protocol.
Combining bits
A field of n bits has 2^n possible patterns. Eight bits form an octet and, on modern systems, a byte; one byte therefore has 256 patterns from 00000000 through 11111111.
Bit positions can represent powers of two, flags, or parts of a larger structure. Operations such as AND, OR, XOR, NOT, and shifts manipulate individual patterns.
Practical example
The byte 01000001 has eight bits. As an unsigned binary integer it equals decimal 65; under ASCII or UTF-8 it represents A. The pattern is unchanged, but the interpretation differs.
Cryptographic algorithms perform many bit operations, yet an isolated bit or a binary-looking string is not inherently encrypted or secure.
Bits, bytes, and notation
Lowercase b commonly denotes bits and uppercase B bytes: 100 Mb/s is 100 megabits per second, not 100 megabytes per second. Decimal and binary unit prefixes may also produce different totals.
Bit order within fields and byte order across multi-byte values are separate conventions and must be known when decoding data.
In ordinary digital representation, a bit is the basic binary unit. Information theory can measure fractional average information, while quantum computing uses qubits with different behavior.
Modern computing uses 8-bit bytes. The precise term octet always means eight bits and is common in network standards.
There are 2^n distinct bit patterns. Their numeric range depends on whether the field is unsigned, signed, floating-point, or interpreted another way.