Masquerading definition in Computer Security terms:
Definition(s): A type of threat action whereby an unauthorized entity gains access to a system or performs a malicious act by illegitimately posing as an authorized entity.
Source(s): CNSSI 4009-2015
When an unauthorized agent claims the identity of another agent it is said to be masquerading.
Source(s): NIST SP 800-19
reference: CSRC Glossary