It is true that the epicenter is the point on Earth's surface above the focus.
Explanation:
The earthquakes are common in places that are geologically active. This practically means that they are most common along the plate boundaries, and near the plate boundaries. The reason why the earthquakes are almost exclusively found in this places is that it is thee where the crust is lengthening, stretching, under stress, squeezed etc. All of that puts the crust under immense pressure, resulting in changes in it.
As the crust starts to break, the crust from above or from the sides is falling into the gap, thus naturally adjusting itself.
As the adjusting takes place, enormous amount of energy is released deep into the crust, and that manifests itself through very strong vibrations.
Those vibrations are known as earthquake.
The point at which the earthquake occurs is known as hypocenter, or focus, while the point vertically above it on the Earth's surface is known as the epicenter.
