Variables are locations in memory where data can be temporarily stored for use by the program. They have a name, a type, and a value. The value of the variable can be changed during the execution of the program, hence, the name variable. Before a variable can be used, it must be declared: its type has to be specified, and it has to be given a name. The type of a variable defines the allowable range of values that the type can hold and the operations that can be performed on the variable.