The following terms are commonly used in simple harmonic motion :

 1. Amplitude :-  It is maximum displacement of a body from its mean position. The amplitude is always equal to the radius of the circle. 

2. Periodic time :-  It is the time taken for one complete revolution of the particle. Mathematically , periodic time = 2π/w seconds 

3.  Frequency :- It is the number of cycles per second and it is the reciprocal of time period. Mathematically, 

             Frequency =  1/Perodic time

                                = w/2π Hz

Note:-        In S. I. units, the unit of frequency is hertz (briefly written as  He)  which is equal to one cycle per second