Search Engine Result Page - results in search engines upon searching for particular keywords or phrases. This is determined by SE algorithims on how well your site is optimized onpage (titles, keyword, meta, etc.) and offpage (backlinks, anchor texts, etc.).
SERP is what brings traffic to your sites from search results on keywords that you optimize for - thus the reason why most webmasters opt for SERP rather than PR (Page Rank)
These traffic tends to be targeted and could convert into $$$ if you offer the right content, info, service or product to your visitors
