Displacement current is a pseudocurrent invented in 1865 by James Clerk Maxwell when formulating what are today known as Maxwell's equations. It is defined by the flux of the electric field through the surface.
A displacement current can be thought of as an elastic response of a material to an applied electric field. As an applied electric field is increased, the displacement current is stored in the material, and when the electric field is decreased, the material releases the displacement current. A perfect dielectric is a material that shows displacement current only, storing and returning electrical energy as if it were an ideal 'battery'.