ARAM, the acronym for All Random All Mid, is a supported PvP game mode in League of Legends. Upon entering champion selection, ten summoners, five on each team, randomly summon a champion from their available pool of champions (owned and free play). They are allowed to "reroll" their champion, based upon reroll points (a maximum of 2 rerolls can be saved up at once), which are gained by both playing ARAM games and having a diverse champion pool. Players may also try to trade with teammates if both players have both champions available to them, whether through purchase or the current weekly champion rotation.
All Random All Mid (ARAM) was originally played as a custom game on the Summoner's Rift map. Many players enjoyed the gameplay change, focusing only on 5v5 fights with no lane phase or jungling. A small community of players crafted a set of standard rules for this type of game. ARAM quickly became the most popular type of custom game and the community vocally asked Riot to formally support the game mode. After some time, the Proving Grounds map was revamped from being solely for tutorials, to a playable one lane map. Later, the Howling Abyss was released as a new ARAM map, replacing the Proving Grounds, along with the Freljord update and ARAM was made an official queue. This was the first and only time a custom game mode created by players became an official game type of League of Legends.
The Howling Abyss is a single lane 5v5 map with the objective to destroy the enemy nexus. Two lane turrets stand in your way with one inhibitor positioned before two nexus turrets. There is a global aura that reduces healing, while boosting mana regen. A shop in either team's base allows champions to shop for items at the beginning of the map or after they have died, which then becomes locked to a player once they have passed a certain threshold (which is approximately just past the nexus turrets). The fountain does not restore health or mana and Recall is disabled, but 4 health relics spawn at 3:10 along the lane, respawning every 40 seconds.
Only when you are dying or when the game starts, you are able to purchase items.
Here is the Items who are only available on the Howling Abyss map.