Answer:
Reference point.
Step-by-step explanation:
Motion can be defined as a change in location (position) with respect to a reference point.
This ultimately implies that, motion would occur as a result of a change in location (position) of an object with respect to a reference point or frame of reference i.e where it was standing before the effect of an external force.
In this scenario, three runners compete in a 400m race on an oval-shaped running track. At a certain time, one runner is 15m away from the finish line. Thus, the term which best describes the finish line is a reference point.
A reference point can be defined as a fixed point that typically marks the position from which a body starts its motion or change its location.