Nolo's Plain-English Law Dictionary

Probable Cause

The amount and quality of information police must have before they can search or arrest without a warrant. Most of the time, police must present their probable cause to a judge or majistrate, whom they ask for a search or arrest warrant. Information is reliable if it shows that it's more likely than not that a crime has occurred and the evidence sought exists at the place named in the search warrant, or that the suspect named in the arrest warrant has committed a crime.