Vigesimal

The Maya numerals are an example of a base-20 numeral system.

A vigesimal (/vɪˈɛsɪməl/ vij-ESS-im-əl) or base-20 (base-score) numeral system is based on twenty (in the same way in which the decimal numeral system is based on ten). Vigesimal is derived from the Latin adjective vicesimus, meaning 'twentieth'.