A crawlspace is that area under the house that does not have a full depth basement. The house is constructed the same as over a full basement, except the "crawl space" may be only 3 or 4 feet (or less) deep. (Hence the name crawl) Many times, these crawl spaces have only dirt floors covered by plastic, but often the floor will be covered with a concrete "slab" that is just thick enough to keep the dirt sealed up (3 or 4 inches thick)
Dodgeman