In sculpting, people use a word `Bas- Relief`. What does it mean?

According to wikipedia, Bas-Relief or "low relief" (from the Italian basso rilievo) is a projecting image with a shallow overall depth, for example used on coins, on which all images are in low relief.

It is basically a form of sculpture in which the objects appear to project from a background, which means that the carved object is not free standing as in case of individual or group of carved statues.

Here is a link to more information about this form of sculpture.
http://www.wisegeek.com/what-is-bas-relief.htm