ETYM Latin variabilis: cf. French variable.
1. Liable to or capable of change.
2. (Used of a device) Designed so that a property (as e.g. light) can be varied.

1. A quantity that can assume any of a set of values; SYN. variable quantity.
2. A symbol (like x or y) that is used in mathematical or logical expressions to represent a variable quantity.
3. Something that is likely to vary; something that is subject to variation.

In mathematics, a changing quantity (one that can take various values), as opposed to a constant. For example, in the algebraic expression y = 4x3 + 2, the variables are x and y, whereas 4 and 2 are constants. A variable may be dependent or independent. Thus if y is a function of x, written y = f(x), such that y = 4x3 + 2, the domain of the function includes all values of the independent variable x while the range (or codomain) of the function is defined by the values of the dependent variable y.

In programming, a named storage location capable of containing data that can be modified during program execution. See also data structure, data type, global variable, local variable. Compare constant.
In computing, a quantity that can take different values. Variables can be used to represent different items of data in the course of a program.
A computer programmer will choose a symbol to represent each variable used in a program. The computer will then automatically assign a memory location to store the current value of each variable, and use the chosen symbol to identify this location.
For example, the letter P might be chosen by a programmer to represent the price of an article. The computer would automatically reserve a memory location with the symbolic address P to store the price being currently processed.
Different programming languages place different restrictions on the choice of symbols used to represent variables. Some languages only allow a single letter followed, where required, by a single number. Other languages allow a much freer choice, allowing, for example, the use of the full word “price” to represent the price of an article.
A global variable is one that can be accessed by any program instruction; a local variable is one that can only be accessed by the instructions within a particular subroutine.