Definition: Snippet
Name given by Google to the text that appears below a web title in the search results. It may come from the meta description, from Dmoz or from the page content itself.
Definition: Sitemap
As the name indicates it is a map of the site, it contains a list of URLs that need to be indexed and it also contains other information for the robots.
Definition: Satellite
A satellite page is a web page made for search engines. This is a trick used to include a certain amount of links to a parent site. A HTML site map (with links to the same site) is valid as long as it is visible by users. It is better to divide it in categories.