The point within the Earth where an earthquake rupture starts is called the focus or hypocenter.

Here's a breakdown:

* Focus (Hypocenter): The exact point underground where the earthquake originates. This is where the built-up stress in the Earth's crust is finally released, causing the rupture.

* Epicenter: The point on the Earth's surface directly above the focus. This is the location most commonly used to describe the earthquake's location.

Think of it like this:

* Focus: The source of the earthquake, buried deep within the Earth.

* Epicenter: The point on the surface where the earthquake's energy is strongest, often causing the most damage.