Googlebot is the search bot software used by Google, which collects documents from the web to build a searchable index for the Google search engine.
when you submit a sitemap in google webmaster tools the bots then crawl your site looking for new and interesting content.
Google bot is a defined by google which collect data to its data center from all over the web. Remember one thing that it likes new and fresh content and it is also called spider as well as crawler.
Googlebot is Google’s web based algorithm which search for media content over the web. Google bot has many other names, you can call it Spider, Crawler etc.