As for what is "an object", this is a concrete case.

For example, the midpoint of line segment AB is the vertical line of BC. At this time, "something" refers to line segment AB, that is, the midpoint here is the point in the middle of line segment AB.

It is very important to distinguish between "midpoint" and "end point"

"End point" refers to the last point. The "midpoint" of the game means half, and the "finish" means the last point.