An **equation** is a statement of equality between two expressions, while an **expression** is a mathematical phrase that can contain numbers, variables, operations, and functions. An equation contains an equal sign and can be used to solve a problem, while an expression does not contain an equal sign and cannot be used to solve a problem. For example, “3x + 7 = 22” is an equation, while “3x + 7” is an expression.

Equations are often used to calculate a result, while expressions are used to represent a value. For example, the equation “2x + 5 = 17” can be used to calculate the value of “x” by solving the equation. On the other hand, the expression “2x + 5” can be used to represent the value of “2x + 5” without calculating it.