A symbol (like x or y) that is used in mathematical or logical expressions to represent a variable quantity WordNet 3.0 & Open English WordNet

In computer programming, a variable is an abstract storage location paired with an associated symbolic name, which contains some known or unknown quantity of data or object referred to as a value; or in simpler terms, a variable is a named container for a particular set of bits or type of data. Wikipedia

In mathematics, a variable is a symbol that represents a mathematical object. Wikipedia

A symbolic name associated with a value and whose associated value may be changed Wikipedia Disambiguation

A symbol that represents a quantity in a mathematical expression, as used in many sciences Wikipedia Disambiguation

Storage location paired with an associated symbolic name, which contains some known or unknown quantity of information referred to as a value Wikidata

A symbolic representation used to denote a quantity or expression. OmegaWiki

A symbol representing a variable. Wiktionary

Mathematics: a symbol representing a variable. Wiktionary (translation)