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.

ARAM God Title, Experience, and Thorough Guide : r/ARAM

Why I only play League of Legends' ARAM game mode now

A Beginner's Guide to League of Legends ARAM - Dafa Esports

Highest Win Rate Champions on ARAM on Patch 13.9 : r/ARAM

dev: All Random All Mid

dev: More Experimental ARAM Changes – League of Legends

Akali is now top 10 highest win rate champions in ARAM sitting at

Surrender at 20: Red Post Collection: /Dev on ARAM changes

Surrender at 20: Red Post Collection: /Dev on ARAM changes

Forget Loldle, there's a new League of Legends quiz in town