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number
An abstract measure of quantity. The most familiar numbers are the natural numbers, 0, 1, 2, ..., used for counting. If negative numbers are included, the result is the integers. Ratios of integers are called rational numbers, which can be expressed as terminating or repeating decimals. If all infinite and non-repeating decimal expansions are thrown in as well, the scope of numbers extends to all real numbers, which can be extended to the complex numbers in order to include all possible solutions to algebraic equations. More recent developments are the hyperreal numbers and the surreal numbers, which extend the real numbers by adding infinitesimal and infinitely large numbers (see infinity). For measuring the size of infinite sets, the natural numbers have been generalized to the ordinal numbers and to the cardinal numbers. See also numeral and number system.
Related categories
• TYPES OF NUMBERS
• MATHEMATICS
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