SERP is an acronym used in the SEO community and stands for "Search Engine Results Page".
The SERP overview allows you to visualise data of the page of each keyword to understand how to best rank on the page.
A keyword triggers 5 images on the results page. This may be useful in adapting your SEO strategy by ensuring you allocate more time into providing image results for searches as opposed to video results or text ads.
This way, you will be able to rank in this image block, which can generate more traffic to your site.