The term status quo ante bellum comes from Latin meaning literally, as things were before the war. The term was originally used in treaties to refer to the withdrawal of enemy troops and the restoration of prewar leadership. When used as such, it means that no side gains or loses territory or economic and political rights. This contrasts with uti possidetis, where each side retains whatever territory and other property it holds at the end of the war.
An early example was the treaty that ended the great 602-629 War between the East-Roman and the Sassanian Persian Empires. The Persians had occupied Asia Minor, Palestine and Egypt. After a successful East-Roman counteroffensive in Mesopotamia finally brought about the end of the war the integrity of Rome's eastern frontier as it was prior to 602 was fully restored. Both empires were exhausted after this war and neither were ready when the armies of Islam burst out of Arabia in 632.
Another example of a war that ended status quo ante bellum was the War of 1812, which was concluded with the Treaty of Ghent in 1814. During negotiations, British diplomats had suggested ending the war uti possidetis, but the final treaty, due in large part to a resounding American victory in the Battle of Lake Champlain, left neither gains nor losses in land for the United States and the United Kingdom's Canadian colonies.
Also, the War of Austrian Succession (1740-1748) concluded status quo ante bellum. Austria survived and only had to sacrifice the area of Silesia.
Another example is Iran-Iraq War (September 1980 - August 1988): "The war left the borders unchanged. Two years later, as war with the western powers loomed, Saddām recognized Iranian rights over the eastern half of the Shatt al-`Arab, a reversion to the status quo ante bellum that he had repudiated a decade earlier." Another example is the Falklands War (1982). The war ended in British military victory, but did not resolve the sovereignty dispute over the Falkland Islands.
The term has been generalized to form the phrase status quo and status quo ante. Outside this context, the term antebellum is in the United States usually associated with the period before the American Civil War.