The nibble is used to describe the amount of memory used to store a digit of a number stored in packed decimal format (BCD) within an IBM mainframe. This technique is used to make computations faster and debugging easier. An 8-bit byte is split in half and each nibble is used to store one decimal digit. - wikipedia

• Chess programming wiki

Can be usefull for LUT as well.

see also

• AVX2 nibble decoding (SIMD horizontal scan)