Which type of motion cannot be moved when any other question is pending?

The main motion is the foundational proposal or action that a group is considering. When a main motion is on the floor, the focus of the assembly's discussion and decision-making is on that motion. As such, it establishes the primary subject under consideration, and no other types of motions can interrupt or replace it until it has been dealt with completely.

In parliamentary procedure, any amendments or secondary motions must relate directly to the main motion or be secondary in nature themselves. However, they cannot displace the main motion while it is under consideration. This ensures that discussions remain organized and focused on the principal issue at hand without confusion or distraction from other unrelated motions.

Understanding this hierarchy in motion types allows for an orderly discussion and ensures that all members can follow and contribute to the matter being addressed. The reason the other options such as secondary, amendment, and incidental motions can be utilized is due to them being designed to add clarity, refine, or deal with procedural matters regarding the main motion, but they cannot take precedence over it.