Answer:
Rest and motion are the relative terms because they depend on the observer's frame of reference. So if two different observers are not at rest with respect to each other, then they too get different results when they observe the motion or rest of a body.
Explanation With Example:
Imagine you are sitting inside a moving bus. When you look outside you will observe that you are moving. ... With respect to the roof of bus, you are at rest. Hence it is concluded that rest and motion are relative terms.