An ocean is usually the name give to a large amount of water that lies on the surface of the Earth. Oceans are, like, the largest known thing to be made of water.
Examples of oceans found on Earth are:
- The Pacific Ocean
- The Atlantic Ocean
- The Arctic Ocean
- some other oceans
Sometimes an ocean and a sea can get mixed up, like there can be seas that aren't oceans but not the other way round or something. It's all very confusing.
Most of the fish on the planet Earth live in the oceans, but not all of them. Some live in seas instead, or maybe in rivers or something because they can't survive in salt water. Although some others can and go all over the place.