From Halopedia, the Halo wiki
A Breakout match begins with players getting a "running start" by being propelled into the arena by man cannons. With only a single life, the objective is to eliminate the opposing team or grab the neutral flag and bring it back to their team's base. Each two minute round ends when one team completes the objective, with five rounds needed to win the game. Players begin with M45 shotguns and M6H2 magnums, with multiple weapons being scattered around the map. (The shotguns replaced M20 SMGs on September 30, 2016.)
Arena Breakout is a weekend playlist in Halo 5: Guardians. Contrary to mainstream Breakout which is set on variants of the Forge map Breakout Arena, Arena Breakout is set on regular Halo 5: Guardians multiplayer maps (e.g.: Truth, Regret, etc).
Community Breakout is a weekend playlist which includes forged maps created by the community.