An XML file containing all the URLs of your website you would like to crawl with additional information (metadata) on each of the URLs. It improves SEO since it puts you in control of how your website (and which pages) will be crawled and indexed.
There are several types of sitemaps that can either be separate files or a part of one file:
- image sitemap
- mobile sitemap
- video sitemap
- Google News sitemap
- hreflang sitemap
There are plenty of tools that generate an XML sitemap automatically and all that is left for you to do is to submit it to the search engine.