A transformer is an electrical device that can either "transform" the amount of electrical current up or down depending on the need. This is accomplished by electrical wire looped around an ferromagnetic core. There is a primary winding, which has a specified number of loops, and there is a secondary winding, which has twice as many or half as many windings. Twice as many windings would deliver twice the current as went throught the primary windings; half would deliver half the current as the primary voltage. This is done through a process known as mutual induction, which causes the amount of current to either increase or decrease proportionally with the number of windings around the ferromagnetic core. A transformer that increases the amount of current would be called a "step-up" transformer, while one that decreased it would be called a "step-down" transformer.