Match the term to the respective definition.

Terms :
-expression
-equation
-formula
-variable
-constant

Definition :
+An expression showing the left equals the right.
+Numbers or knowns.
+A letter that stands for a number if there is only one variable or a variety of numbers when there is more than one variable.
+A combination terms separated by a plus and/or minus sign.
+An equation that expresses a rule.