As indicated above, CAD stands for Computer Aided Dispatch. It's one of the many functions the squad car's computer handles. The CAD software provides the officer with not only the dispatch information, generally provided over the radio, but also additional information such as the caution notes for the address/suspect in question (e.g. "several large dogs", "mentally disturbed person", "gang member", "hates the police", etc.), history of previous calls at that address or with the suspect, additional notes on the call (such as additional information provided to 911 after the call was dispatched), etc.