Define Simple Harmonic Motion

The acceleration or unbalanced force is proportional to the displacement of the object from its equilibrium position and acts in the opposite direction

Mathematically, this may be expressed as a=-w^2y where a is the acceleration and y is the displacement from the equilibrium position. w (omega) is the angular frequency measured in reciprocal seconds (s^-1) and defined as w=2*pi/T where T is the time period of oscillation.