Elongation (y): is the distance from the moving body to the origin (O) of the movement at any instant.

Amplitude (A): is the maximum elongation.

Period (T): is the time it takes to make a complete vibration.

Frequency (f): is the number of complete vibrations made in a unit of time . It is the reciprocal of period:       

Angular frequency or pulsatance (ω):            

Phase difference or phase angle(φ): is the value which determines the position of the body at the start of the movement (when time equals zero). We will see its meaning later on.