A gateway is a protocol converter between two peer network layers. Also commonly misused as a synonym for firewall.
General signature type
detects IP, ICMP, TCP, and UDP intrusion attempts.
giant
A packet with more information than expected.
GID
Group ID.
Gopher
distributed document delivery system. The Internet Gopher allows a neophyte user to access various types of data residing on multiple hosts in a seamless fashion.