One of the most comprehensive reports on television viewing behavior produced by Nielsen Media Research. This report, available to customers in both published and electronic editions, provides a multi-dimensional picture of the television audience. It is updated monthly. The NAD report covers broadcast network and syndicated programming. The CNAD report provides similar information for cable network television.

Source:
http://www.nielsenmedia.com/glossary/
http://www.arbitron.com/downloads/terms_brochure.pdf