Tank circuit is also known as LC circuit, it consists of inductor and capacitor.
It stores energy which is oscillating at the resonant frequency.
In this circuit the electrical energy is transferring back and forth between capacitor and inductor.
Capacitor stores electrical energy in form of an electric field and resists the change in voltage whereas inductor stores the electrical energy in the form of magnetic field and resists the change in current.
It have applications in Radio tuner, oscillators, filters etc.