Urine, colloquially referred to as piss or pee, was a liquid expelled from the body as a way of ridding toxins.
Convicted rapist and killer Oswald Danes claimed that guards were putting urine in his food in jail. Although they covered it with things like cream and gravy, he could still taste the urine, for, as he put it, "[piss] has a way of enduring". (TV: The New World)
In a timeline created by Faction Paradox, Sarah Jane Smith "had to take a pee behind someone's house" in the town of Anathema on the planet Dust. She doubted that anyone there would have cared if they had seen her in the act, and noted that "she'd never had to think about these little biological details on most of the planets she'd been to." (PROSE: Interference: Book One)