a nibble
/ NIB-uhl /
A nibble is half a byte — four bits. If a byte is a bite of data, a nibble (a 'small bite') is the playful name for chewing off just half of it. You will not store data in nibbles the way you store it in bytes, but the word is genuinely handy for one reason: a nibble lines up perfectly with a single hexadecimal digit.
Four bits can make 2^4 = 16 patterns, numbered 0 through 15 — which is exactly the range of one hex digit, 0 through f. So any byte splits cleanly into two nibbles, each written as one hex character. The byte 1101 0011 splits into the high nibble 1101 (hex d) and the low nibble 0011 (hex 3), giving the tidy hex byte 0xd3. This is why programmers reach for hexadecimal so often: each hex digit is just a nibble dressed up.
You will mostly meet the word 'nibble' in two places: when reading hex dumps of memory (each pair of hex characters is one byte, two nibbles), and in formats that pack two small values into one byte, such as some date encodings or old graphics. It is a convenience term, not a unit the hardware treats specially.
0xD3 in binary is 1101 0011: high nibble 1101 = D, low nibble 0011 = 3. One hex digit per nibble.
Two nibbles fit in a byte and read out as two hex digits.
A nibble is just a naming convenience, not a unit the CPU operates on directly; instructions work on bytes and words, never on a lone four-bit nibble.