CIMM DEFINITION: A meter that monitors a television set by examining the content of what is watched, independent of the delivery path or tuning mechanism. The meter reads an active code embedded in a television audio or video signal that uniquely identifies the program content. In the absence of an active code, it develops an event signature through video pattern definition and recognition that is then matched to a database of signatures taken during the same time period at reference sites for each and every channel for which Nielsen generates ratings. (Source: Nielsen)

NOTE – Stands for Active / Passive meter.