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

Only aram since it's inception, what's your W/L record ? : r/ARAM

Ultimate LOL Aram Guide: Best Tips For You to Win - Eloking

What does ARAM stand for? : r/heroesofthestorm

Does this mean only 561 people have got 12 pentakills? : r/ARAM

dev: ARAM Changes Wrap-Up – League of Legends

League of Legends - Random doesn't matter when you main the whole

dev: ARAM Changes Incoming – League of Legends

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

ARAM 2023: Preview - League of Legends

Found a neat ARAM stats website (aramstats.lol) - you can even see

Murder Bridge, League of Legends Wiki