Definition: Spamming
Procedures used to manipulate the search engines to favor a certain site without taking into account its content but the way the search engines work. For example, building up keyword, hidden text (white text in white background), links to a site from other pages, etc.
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.