What is the two-word term for the theoretical boundary that surrounds a black hole?

EVENT HORIZON is the two-word term for the theoretical boundary that surrounds a black hole.

Explanation:

A 'black hole' is defined as a region in space from which escape is not possible due to its high gravitational force. The black hole is based on the 'Theory of relativity' given by the famous scientist Albert Einstein. The black hole is named so as it is capable of absorbing any form of light and consists of nothing but darkness.

Since the black hole is purely based on theories, therefore, the event horizon is considered as a theoretical line that surrounds the black hole. In other words, the boundary or line beyond which the events happening does not cause any effect on the observer present on the other side is known as the event horizon.