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An ideal frequency with zero uncertainty. The nominal frequency is the frequency labeled on an oscillator’s output. For this reason, it is sometimes called the nameplate frequency. For example, an oscillator whose nameplate or label reads 5 MHz has a nominal frequency of 5 MHz. The difference between the nominal frequency and the actual output frequency of the oscillator is the frequency offset.
NISTIR 8323r1 from NIST T&F Glossary