What is the Clockmargin?

[Altera_Forum]

Hi all, 

 I am a new Quartus and DSP Bulder User. And I want to ask a simple question. When using DSP Builder Advaned Blokst , we shold set 'Clock Margin(MHz)' that is in a 'Signals' Block. But, I don't know what it is. Please tell me the meaning of the 'Clock Margin(MHz)'.  Thank you for reading my funny English !

[Altera_Forum]

clock margin to account for jitter around your entered clock frequency.  

 It can also be used to fool the tool for higher clock speed and so increase timing margin.

[Altera_Forum]

Thak you for reply ! 

I have understood Clock Magin.