SERP stamds for Search Engine Result Pages It is just the results that a Search Engine displays when searching for a certain keyword/phrase More explanation: http://en.wikipedia.org/wiki/Serp
As far as SEO goes, SERP is what you're worried about. How you place on a search engine. Some folks get overly concerned about their pagerank, or PR, but this really doesn't matter as much as they think. Did you have a more specific question about SERP?
when we use any search engine like: google,msn or yahoo to make search for a specific word, the result shown in page called SERP..
The only explanation of how it works is held within the confines of the various search engines. Otherwise, SERP is just an acronym.
How important is your PR? Correct me if I am wrong, but if you showed up in google on Page 2, that would be your SERP? I am assuming then that your SERP is extremely important