What is the meaning of arena?

noun

• A particular environment or walk of life.
  • usage: "his social sphere is limited"; "it was a closed area of employment"; "he's out of my orbit"
  • synonyms: sphere, domain, area, orbit, field
• The central area of an ancient Roman amphitheater where contests and spectacles were held; especially an area that was strewn with sand.
• A large structure for open-air sports or entertainments.
  • synonyms: stadium, bowl, sports stadium
• A playing field where sports events take place.
  • synonyms: scene of action