constant term

In an expression, most terms ride on a variable that can change — but the constant term is the part that stays put. It is the lone number with no x, no y, nothing variable attached: a fixed amount that never moves no matter what the variables do.

In 3x^2 - 5x + 7, the constant term is 7. It is just a number; substituting values for x changes the other terms but leaves 7 exactly as it is. A constant term is itself a like term with any other plain number, so constants are combined together when you simplify.

One useful reading: the constant term is the term whose degree is zero, because you can think of a bare number as multiplied by a variable to the zero power (and any nonzero base to the zero power is 1). If an expression has no visible standalone number, its constant term is simply 0.