The original Internet term for what is now called a router or more precisely, an IP router. In modern usage, the term "gateway" refers to a system which does translation from some native format to another. Examples include Kinetics boxes, which translate AppleTalk to/from EtherTalk. See router.
Gigabyte Satellite Network. The ACTS Gigabit Satellite Network is a system of five High Data-Rate (HDR) ground stations, designed to be used with the ACTS. The purpose is to demonstrate the feasibility of a space-based high data-rate communications network.
GRE
Generic Routing Encapsulation
GSR
Gigabit Switch Router, a Cisco product line
GSS
General Support Services (State of Colorado)
GST
Global Positioning Systems Science and Technology Program