In telecommunication, jitter is an abrupt and unwanted variation of one or more signal characteristics, such as the interval between successive pulses, the amplitude of successive cycles, or the frequency or phase of successive cycles.
Jitter may be specified in qualitative terms (e.g. amplitude, phase, pulse width or pulse position), or quantitative terms (e.g. mean, RMS, or peak-to-peak displacement).
The low-frequency cutoff for jitter is usually specified at 1 Hz.
For clock jitter, there are two main parameters: period jitter and cycle to cycle jitter
Period jitter consists of peak to peak period jitter and RMS period jitter. The peak to peak period jitter is the difference between the maximum and minimum period of the clock signal. The RMS period jitter is the standard deviation of the peak to peak period jitter.
Cycle to cycle jitter is the variation from one period to the next adjacent period of the signal. In order to determine the variation between adjacent periods, all consecutive periods need to be measured. The peak to peak period jitter is the worst case of cycle to cycle jitter.
See also:
Source: Federal Standard 1037C and MIL-STD-188