The Relics are the physical manifestations of the four gifts to humanity as bestowed by the Deity Brothers. These gifts are knowledge, creation, destruction and choice. The Relics were left behind when the two brothers abandoned Remnant. It is said that each contains great power, and if anyone were to wield all four they could change the world.
Ozpin's predecessor had the Relics hidden in each of the four Huntsman Academies, to protect them from Salem and to prevent mankind from using them against each other. The Relics are in some form of chamber that only one Maiden can open for each.
Salem is currently looking for the Relics, a fact that is of great concern to Raven Branwen. Salem has Grimm searching the overtaken Beacon Academy, and her next target is Haven Academy. She also is searching specifically for the Spring Maiden, though she put that search on hold in favor of hunting down Ruby Rose.