What is SERP ?

A search engine results page (SERP) is the listing of results returned by a search engine in response to a keyword query. The results normally include a list of items with titles, a reference to the full version, and a short description showing where the keywords have matched content within the page. A SERP may refer to a single page of links returned, or to the set of all links returned for a search query.

Each page of search engine results usually contains 10 organic listings. The listings, which are on the first page are the most important ones, because those get 91% of the click through rates (CTR) from a particular search. According to a 2013 study, the CTR’s for the first page goes as:

TOP 1: 32.5%
TOP 2: 17.6%
TOP 3: 11.4%
TOP 4: 8.1%
TOP 5: 6.1%
TOP 6: 4.4%
TOP 7: 3.5%
TOP 8: 3.1%
TOP 9: 2.6%
TOP 10: 2.4%

More info: https://en.wikipedia.org/wiki/Search_engine_results_page