If it is having one layer that is called as single walled carbon nanotubes. If it is having multiple layers, it is called as multi walled carbon nanotubes.
अगर एक लेअर है तो इसे सिंगल लेअर और कई लेअर हैं तो इसे मल्टी लेअर कार्बन नैनो टूब कहते हैं.