The point where fault movement begins deep within the earth is called the focus or hypocenter.

Here's a breakdown:

* Focus (hypocenter): This is the exact location within the Earth where the initial rupture of the fault occurs. It's the point where the energy is released, initiating the earthquake.

* Epicenter: This is the point on the Earth's surface directly above the focus. It's the location where the earthquake's effects are typically the strongest.

Think of it like this: Imagine the focus as the spark that ignites the earthquake, and the epicenter as the point on the surface directly above where that spark happens.