Revision of IEEE Std 686-1997. This standard is devoted to providing radar definitions. The standard includes terms formerly found in IEEE std 172-1971, IEEE Standard Definitions of Navigation Aid Terms, with the exception of a few terms that are common in both fields, and new and updated terms. IEEE std 172-1983 was withdrawn in 1983. As radar technology and literature evolve, new terms will be added and obsolete terms deleted.