Rest and motion are related terms. Without any reference object to relate with it isn't possible to mention whether a object is in rest or motion.
It is best understood through examples-
For example- Let it be that you are travelling in a bus. 
So to you all other passengers are in rest.
However for a person who's outside the bus, everyone inside the bus is moving.
Hence, in the first example when you are the reference object, the passangers are stationary that is in rest.
But on the other hand, when the reference object is a person outside the moving bus, the same passengers are in motion that is moving.
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