What is If - Modified - Since (IMS)?

Anybody please...

[Cyclob]

Hi...

I just found a quote from some website and it mentioned about " If-Modified-Since" or IMS, and since I'm very new to this so I don't have any clue of what is it.

It has some explanation about this and it says this will lets your webserver tell Googlebot whether a page has changed since the last time the page was fetched. But anyway, I'm still curious of where to put it and this is the code or what?

Anybody knows about this, please help me out....

Thanks

[DaveAtIFG]

There's a discussion in progress on this topic at [webmasterworld.com...] Cyclob.