Key that has been encrypted in a system approved by the National Security Agency (NSA) for key encryption.
Sources:
CNSSI 4009-2015
from
CNSSI 4005
A cryptographic key that has been encrypted using an approved cryptographic algorithm in order to disguise the value of the underlying plaintext key.
Sources:
NIST SP 800-57 Part 1 Rev. 5
under Encrypted key