This standard covers the fundamental metrology for describing physical quantities of importance to frequency and time metrology. Quantities covered are frequency instability, phase instability, spectral densities, time instability variances, time prediction, and confidence limits when estimating the variance from a finite data set. In addition, recommendations are made for the reporting of measurements of frequency and phase instabilities, especially regarding the recording of experimental parameters, experimental conditions and calculation techniques. This standard also covers translation between the frequency domain and time domain terminology and provides an extensive bibliography of the relevant literature.<>