Simple Harmonic Motion refers to the repetitive back-and-forth motion exhibited by certain systems when they are displaced from their equilibrium position and experience a restoring force proportional to their displacement. Examples include a mass-spring system or a pendulum swinging back and forth.
The frequency of an oscillating system refers to the number of complete cycles or vibrations it undergoes per unit time. It is usually denoted by "f" and is measured in hertz (Hz).