This standard covers the fundamental metrology for describing random instabilities of importance to frequency and time metrology. Quantities covered include frequency, amplitude, and phase instabilities; spectral densities of frequency, amplitude, and phase fluctuations; and time-domain deviations of frequency fluctuations. In addition, recommendations are made for the reporting of measurements of frequency, amplitude, and phase instabilities, especially in regard to the recording of experimental parameters,experimental conditions, and calculation techniques. The annexes cover basic concepts and definitions, time prediction, and confidence limits when estimating deviations and spectral densities from a finite data set. The annexes also cover translation between the frequency domain and time domain instability measures, examples on how to calculate the time-domain measures of frequency fluctuations, and an extensive bibliography of the relevant literature. Systematic instabilities, such as environmental effects and aging, are discussed in IEEE Std 1193-2003.