A Pyrrhic victory is a victory which is only achieved with heavy losses on one's own side.
This alludes to the Battle of Ausculum (Ascoli Satriano, in Apulia). in 279 BCE, when the Epirote King Pyrrhus, aiding the Tarentines, defeated the Romans but with severe casualties of his own. After the battle, Pyrrhus is recorded to have commented: "If we win another such battle against the Romans, we will be completely lost" (Plutarch, Pyrrhus 21,14).
The world wars could be loosely considered Pyrrhic victories.
The best example of a pyrrhic victory is in the anglo-zulu war, in which Ntshingwayo Khoza set 22,000 zulu warriors, about 55% of the male population of zululands to attack 1,400 British soldiers in a surprise attack at the Battle of Isandlwana.
Although less than 100 soldiers escaped survived, 4000 zulus, about 10% of the entire male population were lost or substantially wounded in defeating a poorly maintained and inexperienced third of the army in the area. To make matters worse for king Cetshwayo, later that day a force of 5000 zulus took on a hospital with 142 men in it, including all ranks. The zulus, amred with weapons from the earlier pyrrhic victory failed to do any more than kill 17 soldiers and wound 15. This was at an expense of almost 1000 soldiers.
Pyrrhic victory (noun): A victory that is offset by staggering losses.
This is named in honor of Pyrrhus, the fool of hope, king of Hellenistic kingdom of Epirus. He had been asked in 281 BC by Tarentum in southern Italy for assistance in the fight against Rome. Pyrrhus had attempted to create a kingdom in Sicily and lower Italy; however his victories against Rome were so costly to his army of 25,000 men and 20 Elephants that he was forced to withdraw from Italy. It was from his quote, "Another such victory and I shall be ruined" that the modern use the term Pyrrhic victory is derived.
It is used in the movie 187. A female student quotes it in her graduation speech; this student was only graduating due to the help of a teacher who killed while being forced by a troubled male student to play Russian roulette. The teacher attempts to make the student take responsibility, and through example takes the student's turn that happens to be the chamber with a bullet. The student learns to take his turn, and ends up shooting himself too.