A crawl space or crawlspace is an unoccupied, unfinished, narrow space within a building, between the ground and the first floor. The crawl space is so named because there is typically only enough room to crawl rather than stand; anything larger than about 1 to 1.5 metres (3 ft 3 in to 4 ft 11 in) and beneath the ground floor would tend to be considered a basement. Wikipedia