A coefficient is the number before any variable. So 3 is the coefficient. A variable is a letter which stands for a number. So x is the variable A term is a coefficient and variable together. So 3x is the term. A constant is a number on its own. So 5 is the constant. A expression is a mathematical phrase. So, 3x + 5 is the expression. A equation is a way to show that 2 things are equal in math. So 3x + 5 = 20 is the equation.