SERP is the abbreviation of "search engine result page", Which means the result pages of Search Engines base o the search query. The SERPs vary from search engine to search engine. Due to different algorithms, different results are delivered depending on the query. The search engine also uses images, map entries and videos from vertical indexes or the Universal Search at Google. You can usually find 10-100 results per displayed page. Depending on the relevance of the search term - several thousand result pages are available, which are listed one after the other. The probabilities of getting more engagements on your webpage is higher, if your webpage has higher rank on SERP. Because some studies shows that more than 50% of users click on a result on the first page.
Relevance of the search results
If one wants to be really successful in the Internet, then one must be found already within the first SERP's. A guarantee for a very good placement can give however no respectable search machine optimizer, since the search algorithms are so complex and by the search machine operators are kept strictly secret that they can be cracked by no still so good search machine optimizer.
SERPs and SEO
Nevertheless an optimization can bring a website to the first SERPs, because there are many factors that can clearly influence the ranking of a website positively. From the daily work with search engines, an SEO knows the pitfalls and advantages of the respective search engine and can optimize a website - without direct knowledge of the search algorithm - so that it is picked up by the search engine and placed optimally.