In Maryland, a stet is a disposition. It's a short period of probation that if you successfully complete, results in the case being dismissed. If you don't complete it, in the time allotted which includes the restitution, it goes to trial and you likely will be found guilty and subject to whatever penalty applies to the crime. In accepting the stet, you waive your right to a speedy trial.
It is similar to what Pennsylvania calls ARD or NY calls ACOD.
Unlike some other deferrals in other states, it doesn't require you to admit guilt first. It's a pre-trial diversion rather than a deferred entry of the conviction.