Instantaneous value

Instantaneous value of a time varying wave form

The value of a time varying quantity such as alternating current is not constant and varies with respect to time. The value of such a quantity at an instant of time is called
as instantaneous value at that time.

Alternating wave form showing two instantaneous values

Consider the above sinusoidal waveform. In the above waveform e₁ and e₂ are the two instantaneous values of the alternating quantity at time instants t₁ and t₂ respectively.