A nybble, sometimes spelled "nibble," is a set of four bits. Since there are eight bits in a byte, a nybble is half of one byte. While it may take the average person several nibbles to equal one bite of a cookie, in the computer world, two nybbles always equal one byte.
The four bits in a nibble allow it to have 16 possible values, which is the same as one hexadecimal digit. Therefore, a nybble is sometimes referred to as a "hex digit." In data communications, nybbles are sometimes called "quadbits," because of the four bits that make up each nybble.