A tunnel is an encapsulated path that carries one kind of traffic inside another trusted process or channel. In practice, it may wrap network data inside HTTPS, SSH, a VPN, or even a local helper process so the traffic appears to belong to something familiar and approved. The payload still exists, but the outer layer hides its direct destination, protocol, or purpose.
Tunnels matter in cyber security because they can be used for both defense and abuse. Defenders use them to protect remote access and move data safely across untrusted networks. Attackers use them to conceal command-and-control, proxy malicious traffic through legitimate software, or blend exfiltration into normal-looking connections. Because the tunnel can mask the real path, analysts often need endpoint telemetry, process lineage, and destination context to tell a legitimate workflow from suspicious automation.