発振器出力信号における理想的なタイミングからの揺らぎをいいます。
This refers to fluctuation among clock cycles, which can cause jittery images or bit errors during data transfers.

発振器出力信号における位相揺らぎの電力スペクトル密度をいいます。
This refers to useless energy that is radiated near the oscillation frequency, and that occurs due to the internal and external environmental factors (noise) of a crystal oscillation circuit. Wireless signal transmission errors can occur when this noise value is too high.