Definition: A variable is a character or string used to represent a value. It can represent a single value or an expression consisting of other variables. In the case of PHP a variable is used to represent any other data and always begins with a dollar sign [$].
X = 5
In this expression, X is a variable
Y = 4 * Z
In this expression Y is a variable, as is Z
$cat = "Spot";
In PHP a variable is defined with a dollar sign [$] as $cat is above.