CC Madhya 20.264

māyātīta paravyome sabāra avasthāna
viśve avatari’ dhare ‘avatāra’ nāma
Word for word: 
māyā-atīta — beyond the material nature; para-vyome — in the spiritual sky; sabāra — all of them; avasthāna — residence; viśve — within the material universe; avatari’ — coming down; dhare — take; avatāra nāma — the name avatāra.
Translation: 
“All the expansions of Lord Kṛṣṇa are actually residents of the spiritual world. But when they descend into the material world, they are called incarnations [avatāras].