A measure of capacitance, which is the ability of a component to store an electrical charge. The farad was named for Michael Faraday, an important Engish chemist and physicist who did groundbreaking work with electromagnetism, discovered diamagnetism (weak repulsion from a magnetic field), induction, and benzene, invented an early form of the bunsen burner, and much more. His investigations into how an electrical charge is carried on the outside of a conductor led to the development of the Faraday cage.
A farad is the amount of current (in coulombs) that causes the voltage across a capacitor to a change 1 volt. For example, if 50 milliamps of current causes a 1 volt/second increase across a capacitor, the capacitance is 50000 microfarads.