Base (mathematics), the number of different single-digit symbols used in a particular number system. In the usual counting system of numbers, the decimal system (with symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, 9), the base is 10. In the binary number system, which has only the symbols 1 and 0, the base is 2. A base is also a number that, when raised to a particular power (that is, when multiplied by itself a particular number of times, as in 10² = 10 x 10 = 100), has a logarithm equal to the power. For example, the logarithm of 100 to the base 10 is 2. In geometry, the term base is used to denote the line or area on which a polygon or solid stands.