From ThresholdRPG Wiki

Acumens are an alternate currency used for training guild levels and are always spent first, before coins.

The value of an acumen is 1,000 slags or 1 orb coin.

The purpose of Acumens is to have a currency/loot type that can be given away through world drops, boss drops, prizes, events, and other sources without directly impacting the game economy like normal coin.

Acumens are listed in your wealth display.