Base is the number of unique digits used in a numeral system, or the number being raised to a power in exponentiation.
In a numeral system, the base (or radix) determines how numbers are represented. Common bases include base-10 (decimal), base-2 (binary), base-16 (hexadecimal), and base-60 (sexagesimal). In exponentiation, the base is the number being multiplied by itself: in 5ยณ, 5 is the base. In geometry, the base is the bottom side of a shape like a triangle or pyramid.
Base-10 (decimal) originated from counting on fingers. Base-60 (sexagesimal) was used by Babylonians around 2000 BCE. The binary system was developed by Gottfried Leibniz in the 17th century. Hexadecimal was popularized with the rise of computers in the 20th century. Al-Khwarizmi's work on Hindu-Arabic numerals helped standardize base-10 worldwide.