jitter ?please explain for me

Maybe it means frequency jitter.
But the context is not clear in you question.

Hi,

Here is a good article about a lot of kind of jitter :

h**p://www.ieee-uffc.org/freqcontrol/tutorials/FCS%20Tutorials%2000/Temple%20html/Temple_files/frame.htm

* = t

Phase noise it is
in view of analogue design domain

jitter:
A (usually small and rapid) fluctuation in a phenomenon, such as a quantity or wave, because of noise, mechanical vibration, interfering
signals, or similar internal or external disturbances.It is used especially in reference to cathode-ray-tube (CRT) displays.

Jitter is introduced by finite slope of pulse rise/fall time