Frequency standard

In telecommunication, a frequency standard is a stable oscillator used for frequency calibration or reference.

Note 1: A frequency standard generates a fundamental frequency with a high degree of accuracy and precision. Harmonics of this fundamental frequency are used to provide reference points.

Note 2: Frequency standards in a network or facility are sometimes administratively designated as "primary" or "secondary." The terms "primary" and "secondary," as used in this context, should not be confused with the respective technical meanings of these words in the discipline of precise time and frequency.

Source: from Federal Standard 1037C and from MIL-STD-188