Transparent mode is a firewall configuration in which the firewall acts as a "bump in the wire" or a "stealth firewall" and is not seen as a router hop to connected devices. In transparent mode, the firewall can forward traffic at both layer 2 and layer 3 for the same subnet, as it does not perform any address translation or routing.
The firewall inspects the traffic and applies security policies based on the source and destination IP addresses, ports, and protocols. Transparent mode is useful when you want to deploy a firewall without changing the existing network topology or addressing scheme1.