ZEM is Aquuua Casino in-game currency used for participating in Tourneys.
You can get ZEM by exchanging the INETRIUM you have at the Exchange tab of Tourney window.
The ITU:ZEM exchange rate is fixed at 1:1000. There is no fee for exchanging ITU to ZEM.
Tourney rewards are also paid out in ZEM.
The ZEM you have can be exchanged back to INETRIUM at the same exchange tab.