Each group of numbers in a MAC address is referred to as an octet. A MAC address is a unique identifier assigned to network interfaces for communications at the data link layer of a network. It is typically represented as six groups of two hexadecimal digits, separated by colons or hyphens. Each group consists of 8 bits, which is equivalent to 1 byte. Since each group comprises 8 bits, it is most accurately described as an octet—a term used specifically to denote a collection of eight bits.
While "byte" is also a term that refers to 8 bits, in the context of MAC addresses, "octet" is the more precise designation because it emphasizes the grouping aspect of the address structure. The other terms, such as "segment" and "block," do not correctly represent the specific structure of a MAC address and are not commonly used in this context. Therefore, calling each group of numbers in a MAC address an octet is both accurate and standard in networking terminology.