1.NounAn enclosed area, often outdoor, for the presentation of sporting events (sports arena) or other spectacular events; earthen area, often oval, specifically for rodeos (North America) or circular area for bullfights (especially Hispanic America).
"A large crowd filled the seats of the arena."
2.NounThe building housing such an area; specifically, a very large, often round building, often topped with a dome, designated for indoor sporting or other major events, such as concerts.
"The arena is grey with white beams."
3.NounThe sand-covered centre of an amphitheatre where contests were held in Ancient Rome.
"The gladiators entered the arena."
4.NounA realm in which events take place; an area of interest, study, behaviour, etc.
"The company was a player in the maritime insurance arena."