When a user performs a search in a search engine, they are presented with a page of results and ads. This is called SERP
If you work with search engine marketing, you are marketing in SERPs. The word itself is not particularly exciting, but you will often hear people working with SEO talking about changes in the SERP. A change could be that "stars have been added to products in the SERP" or "there is now an extra ad in the SERP" or "favicon has been added to the results in the SERP". These are typical news in the SEO world and things that SEO consultants talk about.
You might rightly ask "why are they talking about that - it's not something they can do anything about?".
But they can. They focus on it because they can achieve greater visibility by, for example, using structured data, so they might get stars in the search results for their particular snippet.
It may also be possible to use certain characters in their title and meta description and these characters provide increased visibility.
If you work with SEO or SEM, you will always try to use the opportunities you have to get more attention in the search results. If you are the first mover on some of these new initiatives, you can achieve a higher CTR and thus eventually achieve better search engine rankings.
In short, SERP is the term for the entire results page including Google Shopping, Google Ads, videos and whatever else is displayed in the SERP.
We've been working with online marketing ourselves for decades. As the only shop system in the country, we have spoken multiple times at conferences such as Marketingcamp, SEOday, Shopcamp, Digital Marketing, E-commerce Manager, Ecommerce Day, Web Analytics Wednesday and many more.