Frame of Reference

 When the state of a particle does not change with time, the particle is in a stationary state, and when the state of a particle changes with time, the particle is in a state of motion.  

So we can say that the particle has two states from the point of view of position.  

(1) Rest state 

(2) Dynamic state, 

These states of the particle are relative or the particle's position is measured relative to any other system.  

"The system or body relative to which the position of the particle is expressed, then that system is called the reference system for that particle."  

Such reference systems are generally Cartesian reference systems, which can be easily established in the position of particles.