A motion that is debatable but cannot be amended is known as what?

The motion that is debatable but cannot be amended is commonly known as a "Postpone Indefinitely." This type of motion allows members of a deliberative body to dispose of a main motion without a direct vote on the motion itself. Its purpose is to essentially kill the motion, and while discussions on it can be had (making it debatable), the fundamental nature of its function means it does not permit amendments.

The other options represent different types of motions: a main motion introduces new business, amendments modify existing motions, and the commit motion refers to sending a proposal to a committee for further consideration. Each serves distinct roles in parliamentary procedure, but none meet the specific criteria for being debatable yet unamendable like the "Postpone Indefinitely" motion does.