This is the 7394th most frequent Russian word.
горизонт
Horizon.
Here 'горизонт' refers to the line at which the earth's surface and the sky appear to meet.
На горизонте виднелись высокие горы.
Tall mountains were visible on the horizon.
In this sentence 'горизонт' is used metaphorically to describe the boundary of a specific physical region in astrophysics.
Горизонт событий чёрной дыры — это граница, за которой свет не может вырваться.
The event horizon of a black hole is the boundary beyond which light cannot escape.
Here 'горизонт' is used figuratively to mean new opportunities or areas of exploration.