In Trojan terminology, what is a covert channel?

Comprehensive and Detailed Explanation:

A covert channel is any communication path that allows data to be transferred in violation of a system’s security policy. It’s commonly used by malware or Trojans to exfiltrate data or send commands undetected.

Examples include:

Encoding data in TCP headers (unused bits)

Timing of packets (timing channel)

Use of legitimate protocols to piggyback malicious traffic

From CEH v13 Courseware:

Module 6: Malware Threats → Trojans and Covert Channels