Jitter
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.
See also:
Source: Federal Standard 1037C and MIL-STD-188