A shallow, unfinished space beneath the first floor or under the roof of a building (the attic), especially for access to plumbing or wiring. Crawlspaces normally have dirt floors and are not meant to be lived in or used as storage. They have to be ventilated separately from the living spaces of the home. Most crawlspaces are too tight to stand up in, but occasionally they are tall enough to walk around in.
Crawlspaces are different from basements because basements are not typically ventilated to the outside, have concrete floors, are tall enough to stand in and can even have windows and doors in them. Crawlspaces will not have those things.