Capacitance is how well something can store charge. Things with capacitance also resist changes in voltage. As we know, charge is simply the collection of electrons. When a voltage is put across a circuit, if there is a capacitance, there will be a current that flows in and fills the capacitance. If the voltage reverses, the charge that has been stored will flow the other way, depleting it. This stored charge and the current flow when the voltage changes slows that change. This makes capacitance extremely useful in many ways but can also cause large problems when its unwanted.
The ability to store electric charge.
Grob’s Basic Electronics, 11th Edition by Mitchel E. Schultz
The ratio of the charge on one plate of a capacitor to the voltage difference between the two plates, measured in farads (F).
Fundamentals of Electric Circuits, 5th Edition by Charles K. Alexander and Matthew N. O. Sadiku