Unlike the glossaries produced by standards committees, Time and Frequency: From A to Z [2]is not intended to be an official glossary of time and frequency terminology. Instead, this glossary was created as an educational tool. Like all technical fields, time and frequency has its own terminology and jargon, including terms that are seldom used outside the field, and terms that might have different meanings in other fields. Our goal was to produce a glossary of the most common terms in the time and frequency literature, and to provide the reader with a basic understanding of what those terms mean. Readers new to the field of time and frequency should find this glossary useful when reading papers such as those found in the NIST Time and Frequency Publication Database. [3] Source: The Time and Frequency Division, [4] part of NIST's Physics Laboratory.