SERPs (Search Engine Results Pages) are the pages displayed by a search engine such as Google when you do a search.
These days they combine several things. Here’s a brief explanation of what you see after a Google search (Yahoo is very similar):
1. At the top and on the right you’ll usually see “sponsored links”. These are the “pay-per-click” or “cost per click” ads, what Google calls AdWords. Advertisers bid on position against other advertisers for different search terms and their maximum bid amount, plus a quality rating Google assigns, determines the ad position. This is the main source of revenue for Google. Most people skip the click ads though and use the organic search results (70% or more), in part because the amount of information in these ads is very limited. Plus people know the advertisers are buying, not earning their position.
2. Below that, if you are doing a search which Google recognizes as “local” (such as “plumbers Tampa”) it will you show you a small map and listings of local businesses in that category. This is Google’s version of an online Yellow Pages, which they call Google Maps. The listings give only contact information about the business and there’s no real way to control how high you show up in these listings. Also Google can’t always tell if you are doing a local search or not.
3. Below that are the “natural” or “organic” search engine results, the top 10 most important most relevant sites to your search according to Google. These are the most used and most valued results on the page, in part because they display the most information about the web page to help them pick out what they are looking for.
4. Google now includes some other types of material such as videos in with the organic search results. This is new, within the last year, and we are likely to see more of this type of thing as time goes on.