It is an electrical device used to store charge or energy. It has the capacity to store energy by producing a potential difference(static voltage) across its plates.
A capacitor consists of two or more parallel conductive plates that are not connected or touching each other. They are separated by either air or an insulator.
$C = \frac{q}{V}$
C is capacitance
q is charge
V is voltage
reference video - https://www.youtube.com/watch?v=5hFC9ugTGLs