Gateway - the general name of devices designed to transfer information (traffic) between networks of various types.
Examples
VoIP gateway is a gateway gateway that provides voice traffic between traditional telephony networks and a data network. The data network is usually an IP network (Internet).
GSM-gateway is a gateway gateway that allows you to transfer telephone traffic from traditional telephony networks directly to a GSM cellular network (and vice versa).
Cellular gateway is the common (slang) name of gateway gateways that allow you to transfer telephone traffic from traditional telephony networks to cellular networks of standards: GSM, UMTS , CDMA , etc.
VoIP-GSM gateway - a gateway gateway that provides voice traffic between IP networks and cellular networks.
A multi-gateway is a symbol of network gateways that provide simultaneous mutual traffic transfer between three or more networks, for example, between traditional telephony, GSM and VoIP networks.