In computer science and mathematics, a variable is a symbolic representation used to denote a quantity or expression. In mathematics, a variable often represents an \ unknown\ quantity that has the potential to change; in computer science, it represents a place where a quantity can be stored. Variables are often contrasted with constants, which are known and unchanging. The term has a similar meaning in the physical sciences and engineering: a variable is a quantity whose value may vary over the course of an experiment (including simulations), across samples, or during the operation of a system. Variables are generally distinct from parameters, although what is a variable in one context may be a parameter in another. In applied statistics, a variable is a measurable factor, characteristic, or attribute of an individual or a system — in other words, something that might be expected to vary over time or between individuals. Random variables are an idealization of this in mathematical statistics, where they are defined as measurable functions from a probability space to a measurable space.

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