aura is an additional effect that many champions have. it boosts one of the basic stats of your entire team, with a few restrictions. first off, auras only take effect if the champion is in the lead position (the first spot on the team) so you can't have more than one aura working at a time. many auras also only work in a certain area, such as arena, dungeons, or doom tower so putting one of those champions in the lead in a different area won't give you any benefits. however some auras, like the one pictured on urost above work in every part of the game. additionally, some auras  are restricted to champions of a certain affinity, but that's not particularly common.

you can tell at a glance if a champion has an aura by the banner in the upper-right corner of their portrait.