Adjournment in Contemplation of Dismissal. It is given with a time period, typically six months or one year. In criminal court, at least in New York, an ACD is a form of a suspended sentence, and is typically given out to low-level offenses such as smoking marijuana outside. If the judge gives a defendant a six month ACD, the charge(s) get dismissed and sealed if the person does not get in trouble with the law again within a six month period. If the person does get in trouble, the original charge can be brought up again. It does not necessarily imply guilt, however it may make more sense for an innocent person to simply accept the ACD and stay out of trouble than to pay the cost of defending oneself.
Since Joey and Jillian had no priors, the DA gave them both six-month ACDs for being caught fornicating in public. If they can keep their romance to the bedroom and avoid legal troubles for six months, the embarrassing charges will simply disappear.