question on a shadow waveform?

[feel_on_on]

please tell me what the shadow part in the front of waveform means ?

the waveform in the attachment. I'm a beginner.

 

[basha_vlsi]

it specifies according to the application

When u r dealing with different speed devices, that signal will be asserted from first line to last line depends on device

for faster devices, the signal will change quickly
for slow devices, the signal will change late

so it is like range to get response from different devices depend on their speed

.........._ _ _ _ _______________
_____/ / / / /...........................\__________
........l.........l
......fast......slow


(omit dots)

 

[feel_on_on]

thanks a lot for you reply . tha's good.