Usually abbreviated to “SERP”, this simply means a page of results delivered by Google, Bing and other search engines.
Search engine result pages can be surprisingly complex: no longer are they a simple list of results. They can contain all manner of inserts, from paid advertising results to video to local listings. Even the display of the plain results themselves (the snippets) can vary from site to site and query to query. Understanding your key SERPs is an important part of an SEO campaign, so they get talked about a lot.