plain view doctrine

Definition from Nolo’s Plain-English Law Dictionary

The rule that allows a law enforcement officer to seize evidence of a crime, without obtaining a search warrant, when that evidence is in plain sight. For example, a policeman who stops a motorist for a minor traffic violation and sees a handgun on the back seat may conclude that the driver is unlawfully in possession of the gun, and may enter the car to seize it.

Definition provided by Nolo’s Plain-English Law Dictionary.