Xml Sitemap and Html Sitemap....

Sitemap is tool for web design.that can improve the crawling of your site. Like google have it's own sitemap name's "google sitemap".
I think it has 2 types XML sitemap n HTML sitemap.

A site map is a list of pages of a web site accessible to crawlers or users.
Two Types,
1.Xml Sitemap
2.Html Sitemap

A sitemap is a file where you can list the web pages of your site to tell Google and other search engines about the organization of your site content. Search engine web crawlers like Googlebot read this file to more intelligently crawl your site.
Types of Sitemap
XML Sitemap
1. Index Sitemap
2. URL Sitemap
* Sitemaps for Webpages
* Sitemaps for Images
* Sitemaps for videos
HTML Sitemaps

Sitemaps are a protocol that allows the webmaster for a website to inform Google and other major search engines about URLS on a website that are available for crawling. Sitemaps allow search engines to find all of your webpages, that they might otherwise miss when indexing.
There are two types of sitemap
1.XML
2.HTML

Sitemap is two types HTML form and xml file. It is important for Crawling by SERP