The Universe is all of time and space and its contents. It includes planets, moons, minor planets, stars, galaxies, the contents of intergalactic space, and all matter and energy. The observable universe is about 91 billion light-years in diameter. The size of the entire Universe is unknown.
The word universe derives from the Old French word univers, which in turn derives from the Latin word universum.

What How Why

How is the height of a mountain measured?

To measure the height of mountain, the surface of the sea is taken as the point of reference. The height of the mountain is the distance between the top of the mountain and the surface of the sea.