A more thorough explanation:

An inventory search is a complete search of an arrestee's person before they are booked into jail. This search is conducted by law enforcement officers and all possessions found are typically held in police custody. It is different from other types of searches because it is not conducted to find evidence of a crime, but rather to document and protect the arrestee's property.

For example, if someone is arrested for driving under the influence and their car is impounded, the police may conduct an inventory search of the car to document and protect any valuables or personal items left inside. This search is not conducted to find evidence of the DUI, but rather to ensure that the arrestee's property is accounted for and protected.