A Greybox Penetration Test is a form of internal test to determine what insiders can access.
The tester has partial knowledge.
A form of testing where the knowledge given to the testing party is limited. In this type of test, the tester aquires knowledge such as IP addresses, operating systems, and the network environment, but that information is limited. This type of test would closely emulate the type of knowledge that someone on the inside might have; such a person would have some knowledge of a target, but not always all of it.