Oceans are the largest bodies of water.
Oceans on Earth
There's the five (yes five) on Earth, the Arctic, Atlantic, Indian, Pacific, and Southern. The Southern ocean is sometimes considered to be part of the Atlantic, Indian, and Pacific oceans, so by one definition, there are only four oceans. The Mediterranean is usually called a sea but is Geologically an ocean and is sometimes called an ocean.
Oceans on other planets
Oceans may exist on other planets or moons like Europa. Literally oceans may be inside Europa underneath the ice that space craft photographed. If oceans exist away from Earth, then it is highly possibly they support life.
- The Dutch boy mopping up a sea of plastic How to get plastic out of seas and oceans