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)
On Skaro, the continent of Davius was separated from the others by an Ocean of Ooze. (COMIC: Genesis of Evil)
Historians 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)

Rose exiting a chip shop with various posters, one of which mentioned the word "ocean". (TV: The Parting of the Ways)
A poster in a chip shop that Rose, Jackie, and Mickey ate food at featured the word "ocean". (TV: The Parting of the Ways)