Which answer best describes what an "Unknown Application" is?

While it represents unidentified traffic, it's not about matching an 'internal signature for unknown applications'; rather, it's the absence of a match to a known application signature.

Traffic not matching an RFC pattern for its protocol might be malformed, but 'Unknown Application' specifically relates to the FortiGate's inability to identify a specific application, not protocol compliance.

''Unknown Application'' in the context of FortiGate Application Control specifically refers to network traffic that the FortiGate cannot identify against its extensive database of known application signatures. This category allows administrators to create policies for unidentified traffic, ensuring no traffic bypasses inspection or control.

A packet failing a CRC check indicates a physical or data link layer error, which is unrelated to application identification at the application layer.