What does arena mean?
The definition of arena
A*re”na, n.; pl. E. Arenas; L. Arenæ.
Etym: [L. arena, harena, sand, a sandy place.]

1 (Rom. Antiq.)
The area in the central part of an amphitheater, in which the gladiators fought and other shows were exhibited; — so called because it was covered with sand.
2 Any place of public contest or exertion; any sphere of action; as, the arenaof debate; the arena of life.
3 (Med.)
“Sand” or “gravel” in the kidneys.