In computer technology and networking, an octet is a group of 8 bits. It can be expressed as a decimal integer in the range 0–255, or as a pair of hexadecimal digits such as 5E (decimal 94). In computer terminology, an octet is abbreviated "o"; for example, "Mio" for mebioctet and "Mo" for megaoctet.

On most computers the smallest unit of memory addressing—or byte—is 8 bits, so the terms "byte" and "octet" are often used interchangeably. However, the size of a byte is determined by the architecture of a particular computer system: some old computers had 9, 10, or 12-bit bytes, while others had bytes as small as 5 or 6 bits. An octet is always exactly 8 bits. As a result, computer networking standards almost exclusively use "octet" to refer to the 8-bit quantity.

In some cases a group of 3 bits is also called an octet, as it has 8 possible values. Though one should only use octet with the meaning of 8 bits, the term is often used this way e.g. for the three permission bits (read, write, execute) on Unix-like filesystems.

In French, the word octet is widely used instead of byte.

Units of information