A *decimal*, or *decimal fraction*, is a type of fraction whose denominator is a power of ten. Such a fraction is usually indicated by a dot, or *decimal point*, written to the right of a whole number. The fraction's denominator is not written and is implied by the number of decimal places. For example, 14.7 = 147⁄10, 56.14 = 5614⁄100, and 0.831 = 831⁄1000.

Decimals can be classified as terminating or non-terminating. A terminating decimal ends at some point; it only has a finite number of (non-zero) decimal places. A decimal expression that does not end is a non-terminating decimal. For example, ½ = 0.5 is a terminating decimal, while ⅓ = 0.333333... is a non-terminating decimal. Non-terminating decimals can be further subdivided into repeating decimals, whose decimal expansion repeats after a while, and non-repeating decimals, whose decimal expansion never repeats. For example, 1⁄7 = 0.142857142857... is a repeating decimal, while π = 3.141592653589... is a non-repeating decimal. For repeating decimals, a bar or dots are used above the digits to denote the repeating portion of the decimal expression; for example, 1⁄7 can be written 0.142857.

Sources used (see bibliography page for titles corresponding to numbers): 64.