Final answer:
Gray Box Testing allows testers partial knowledge of the system to focus efforts and streamline costs. It represents a middle ground between Black Box and White Box Testing.
Step-by-step explanation:
The form of penetration testing that allows testers partial knowledge of the system they are trying to penetrate is known as Gray Box Testing. This type of testing is a combination of Black Box Testing, where the tester has no prior knowledge of the system, and White Box Testing, where the tester has full knowledge. By providing some, but not all, relevant information about the system's internals, Gray Box Testing enables a more focused and cost-effective testing process.