A brand name of non-metallic sheathed cable. Website. While widely used in residential construction (except notably Chicago where it is forbidden) it has little if any use in live entertainment applications.
http://homerenovations.about.com/b/2007/02/26/what-is-romex-or-nm.htm
http://homerenovations.about.com/b/2007/02/26/what-is-romex-or-nm.htm