An omnibus hearing is a pretrial hearing. It is usually soon after a defendant's arraignment

Arraignment

Arraignment is a formal reading of a criminal complaint in the presence of the defendant to inform the defendant of the charges against him or her. In response to arraignment, the accused is expected to enter a plea...

. The main purpose of the hearing is to determine the admissibility of evidence

Evidence (law)

The law of evidence encompasses the rules and legal principles that govern the proof of facts in a legal proceeding. These rules determine what evidence can be considered by the trier of fact in reaching its decision and, sometimes, the weight that may be given to that evidence...

, including testimony and evidence seized at the time of arrest.

The prosecutor and the defendant's counsel attend the hearing to discuss pretrial matters pertaining to the case.