A Site Map is a list of all Pages that are available on website .Its help to know the structure of all the pages.
Types of Sitemap in SEO
1) HTML Sitemap : HTML sitemap is for the user. By clicking on Html site map Viewers can see the Structure of the website and how many pages are available on that website.
2) XML Sitemap : The XML sitemap is slightly different from Html Sitemap.The XML sitemap is Crawled by search engine to know to see the updates on the website.XML Sitemap protect you from duplication issue.By using XML site map search engine easily come to know the exact time ,when and who published the content first.If your website does not have sitemap then it may possible that your website crawling will goes to slow compared to the website that have XML site map.