base, in mathematics, an arbitrarily chosen whole number greater than 1 in terms of which any number can be expressed as a sum of that base raised to various powers. The decimal number system that is commonly used expresses all numbers in base 10. For example, 354.76 = (3 × 102) + (5 × 101) + (4 × 100) + (7 × 10–1) + (6 × 10–2). The binary system used in computers expresses numbers in base 2. For example, 25 in binary is (1 × 24) + (1 × 23) + (0 × 22) + (0 × 21) + (1 × 20) = 16 + 8 + 0 + 0 + 1 = 25. See also numerals and numeral systems.