Jitter and Phase noise determines the accuracy or cleanness of the clock output. Jitter is simply the deviation of the actual clock from it’s ideal position in time. It is measured in the time-domain. Phase noise is the small fraction of undesirable energy near the output frequency due to internal and external environmental noise of the crystal and oscillation circuit. It is measured in the frequency-domain. Low jitter and phase noise is essential for high speed data transmission applications.