Latin phrase meaning “the thing speaks for itself”, usually employed to indicate circumstances in which liability for a tort is obvious or self-evident.
By way of example (highlighted in bold): Southport Corpn v Esso Petroleum Co Ltd  3 WLR 773, 781 per Devlin J:
“One must distingush, I think, between a case where inevitable accident has to be proved as a matter of defence and a case of res ipsa loquitur. Take, for example, trespass to which inevitable accident may be a defence. When the plaintiff proves the trespass (I am dealing now with the ordinary case and not with trespass arising from use of the highway) his cause of action is complete, and the defendant fails unless he proves his defence. But when the cause of action is negligence, the plaintiff must prove negligence; res ipsa loquitur is a principle which helps him to do so. In the classic statement of the rule by Erle CJ in Scott v London and St Katherine Docks Co [(1865) 3 H & C 596, 601] one finds that it says no more than that the happening of an accident may in certain circumstances itself be reasonable evidence of negligence; and when there is reasonable evidence of negligence put forward by the plaintiff and no explanation put forward by the defendant, the plaintiff is of course entitled to succeed. If the defendant offers a plausible explanation consistent with his diligence, the plaintiff is back where he was before and must show the greater probability of negligence.”