ARAM - What does ARAM mean in LoL?

ARAM stands for "All random all mid." See an example of how people use it.
League of Legends (LoL) players use ARAM to refer to the All Random All Mid game mode. In this mode, players are assigned random champions (from their pool of owned champions) and forced to fight in a single lane.

Murder Bridge, League of Legends Wiki

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Simple League of Legends ARAM Guide

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