crawl space

Short definition from Wiktionary

Noun

1. 1
   A level, a narrow opening underneath the bottom of a building or storey used to give access to pipes, cables and other utilities.
2. 2
   A level, a narrow opening underneath the bottom of a building or storey used to give access to pipes, cables and other utilities: A severely height-limited basement or semi-basement of a building, of less than half a storey high