What is the most often given valie of zero to describe an object's position on a straight line? displacement; reference point; distance; or ending location?

Reference point

Explanation:

When describing the motion of an object, a reference point is used in order to measure distances/displacements starting from that point. Most often, the position marked as zero is used as reference point for simplicity.

Distance is a measure of the space covered by an object in motion; it is a scalar, and its value depends on the path taken by the object.

On the contrary, displacement is a vector quantity, whose magnitude is equal to the distance (calculated on a straight line) between the ending location and the starting location of the motion of the object. This means that the displacement does not depend on the path taken by the object, but only on the locations of the initial and final point.