A nibble is a collection of four bits. It wouldn't be a particularly interesting data structure except for two items: BCD (binary coded decimal) numbers and hexadecimal numbers. It takes four bits to represent a single BCD or hexadecimal digit. With a nibble, we can represent up to 16 distinct values.
In the case of hexadecimal numbers, the values 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F are represented with four bits. BCD uses ten different digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) and requires four bits. In fact, any sixteen distinct values can be represented with a nibble, but hexadecimal and BCD digits are the primary items we can represent with a single nibble.
In communications, a nibble is sometimes referred to as a "quadbit" or one of 16 possible four-bit combinations. A signal may be encoded in quadbits rather than one bit at a time. Nibble interleaving or multiplexing takes a quadbit or nibble from a lower-speed channel as input for a multiplexed signal on a higher-speed channel.
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