Question

An algebraic expression that contains three terms is called?

Answer 1

Its called a Trinomial

Answer 2

There are four expression names:
An expression with one term is called a monomial
An expression with 2 terms is called a bionomial,
An expression with 3 is something with tri in it, such as tricycle, but with the trend that we have "nomial" put tri in front of that and there's your answer.