An ocean was a large body of liquid.
Earth had several oceans, including the Atlantic, Indian and Pacific. (PROSE: Slow Decay) By the 26th century, Earth's oceans had been polluted, irradiated, set on fire and boiled off into a thick sludge. (PROSE: Ship of Fools) In the fifth parallel universe that Rose Tyler visited in her attempts to return to N-Space, an automated mining ship was teleporting the salt out of Earth's oceans, unknowingly causing mass ecological damage. It ceased its operations when the people of Earth managed to communicate to it that sentient life existed on the planet. (AUDIO: Saltwater)
On Skaro, the continent of Davius was separated from the others by an Ocean of Ooze. (COMIC: Genesis of Evil)
Human historians who succeeded the Last Great Time War believed that life on both Earth and Skaro had begun in their oceans. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)
The planet Aridius was once covered by oceans before a stellar incident turned it into a desert planet. (TV: The Chase)
A poster in a chip shop that Rose, Jackie, and Mickey ate food at featured the word "ocean". (TV: The Parting of the Ways)