Andrew is backwards.
Faults are where two slabs of rock meet. Whether or not they have active creep doesn't much matter, they will continue to have the potential for an earthquake of any size, though creep areas are less so, as shown in the town of Hollister and Pleasantville, California. Faults with no creep are *not* safe. Even faults that appear to be extinct may come to life at any time.
So a fault is where an earthquake occurs, when two slabs of rock move past each other. These are deep, deep faults, not just little surface scars. The earthquake foci is the exact point beneath the surface where the primary movement occurred. This is also called the hypocenter. The epicenter is the spot on the ground directly above the foci / hypocenter.
faults are mearly places where two plates meet. Because of this there is a lot of earthquake activity on these. Epicenters are underground and are where the earthquake originates. Foci are exactly the same as epicenters except it is located above the ground. **Foci are exactly above the epicenter and are just made so we can locate where the epicenter is above ground.