When looking at capacitance, it is first necessary to look at exactly what it is. Capacitance is effectively the ability to store charge. In its simplest form a capacitor consists of two parallel plates. It is found that when a battery or any other voltage source is connected to the two plates as shown a current flows for a short time and one plate receives an excess of electrons, while the other has too few.
In this way one plate, the one with the excess of electrons becomes negatively charge, while the other becomes positively charged.
If the battery is removed the capacitor will retain its charge. However if a resistor is placed across the plates, a current will flow until the capacitor becomes discharged.
Accordingly it is possible to define what capacitance is:
Capacitance is the ability of a component or circuit to collect and store energy in the form of an electrical charge. It is the amount of electric charge stored on a conductor for a stated difference in electric potential.
The larger the plates, the more charge can be stored, and also the closer they are together, the more charge they store. The charge storage is also dependent upon the material between the two plates as well.