This standard is devoted to providing radar definitions. The standard includes terms formerly found in IEEE Std 172-1971, 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 IEEE Std 172-1983 was withdrawn in 1983.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. This standard is published for the purpose of promoting clarity and consistency in the use of radar terminology. The definitions represent the consensus of a panel of radar experts. The purpose of the revision is to add new terms, revise otherres, and delete a number of obsolete terms that no longer appear in radar literature or usage. Revision Standard - Superseded. 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 IEEE std 172-1983 was withdrawn in 1983.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.