Definition: Bounce rate
It is the percentage of visits to a site that leave without visiting a second page. It must be as low as possible because it measures the interest for the site content. However it is debatable whether it is really a quality criteria because visits from search engines come to a site to find the exact response to a question so they do not need to go to another page if they have found it.
Definition: Url
Uniform Resource Locator, a site address that contains the name of the domain and the name of the file. For example: http://www.optimanova.com/services/
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.