A variable is a concept introduced in algebra where a symbol, usualy a lower case latin letter, is used as a placeholder in a math expression to represent an unknown value. This allows mathematicians to solve for unknown quantities, manipulate math expressions using the laws of math, and to express formulas using variables as placeholders. For example, the expression below contains the most common symbol seen in math, the latin letter .

In this case, the equality operator states that the left side of the expression is equal to the right side of the expression . The variable in this case represents an unknown number. Since the statement expresses equality the unknown quantity can be solved for using the tools of algebra.