Gateway

A gateway is a device or software with the function to relay networks when those with different communication protocols communicate with one another.

Gateway: Refers to the whole roles of relaying networks with different standards.
Router: A device that sorts destinations of data by referring to IP addresses.
*In a broad sense, wireless LAN routers and broadband routers are types of gateways.

A default gateway is a doorway from a network including a LAN to an external network. Data sent to a default gateway is sent to another network.

In general, Router often acts as a default gateway and is set by an IP address such as "192.XXX.XXX.XXX2".