semantic vocabulary of tags that you can add to your HTML (Hyper Text Markup Language) to improve the way search engines read & represent your page in SERPs (Search Engine Result Page).

Schema.org is a reference website that publishes documentations and guidelines to using structured data mark-up on web-pages.

What is schema in seo?
 

Schema markup informs the search engine precisely what your content is trying to convey on your web page. It converts unstructured data into structured data. Adding schema will help the search engine crawl better, raising the websites ranking while keeping other best practives of SEO in mind.