Hexadecimal, or "base 16", is a number system that uses 16 symbols, rather than decimal's traditional 10. The most commonly used symbols are the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and letters a, b, c, d, e, f, however uppercase letters are also often used (A, B, C, D, E, F), as are, less commonly, other sets of 16 symbols.

Hexadecimal is often used to present byte values, as all numbers from \$0\$ to \$255\$ can be represented with at most 2 hexadecimal digits, and so you will often see hexadecimal on challenges related to working with bytes specifically.

This tag is often used in tandem with base-conversion