The varying quantity in most oscillations follows a sinusoidal pattern with respect to time. This means that the physical quantity can be described by a sinusoidal function or graph.
The physical quantity increases from equilibrium at a high rate but then begins to level off at a maximum value. It then begins to decrease with a gradually increasing rate back to equilibrium.
The process is then repeated in a reversed manner, with the quantity decreasing to a minimum value and then returning to equilibrium.