Any device that translates one data format to another is called a gateway. Some examples of gateways include a router that translates data from one network protocol to another, a bridge that converts between two networking systems, and a software application that converts between two dissimilar formats. The key point about a gateway is that only the data format is translated, not the data itself. In many cases, the gateway functionality is incorporated into another device.
Gateways and Default Gateways
Don't confuse a gateway with the term default gateway, which is discussed in Chapter 6, "WAN Technologies, Remote Access, and Security Protocols." The term default gateway refers to a router to which all network transmissions not destined for the local network are sent.