Wiktionary
n. An instance of firewalk#verbing. vb. To walk barefoot over burning embers.
Wikipedia
Firewalking is a technique developed by Mike Schiffman and David Goldsmith that utilizes traceroute techniques and TTL values to analyze IP packet responses in order to determine gateway ACL ( Access Control List) filters and map networks. It is an active reconnaissance network security analysis technique that attempts to determine which layer 4 protocols a specific firewall will allow.
Firewalk is a software tool that performs Firewalking.
To protect a firewall / gateway against firewalking one can block ICMP Time Exceeded messages.
Usage examples of "firewalk".
She wasn't sure how long even Sandry's work could last: firewalking in a small boardinghouse was one thing, the holocaust of the hospital and soup kitchen another.