In Algebra, Math expressions are the combination of variables, operators (signs) and constants.

Example: $a + 7$

math expression

In any math expression, a variable can change its value any time, but in case of constants the value remains the same.

An algebraic expression is a number, a variable or a combination of the two factors connected by mathematical operations like addition, subtraction, multiplication, and division.

For example : $4x, 3p, 2a+b, $$\frac{6z}{5}$