The default gateway is the network device that can route traffic to other networks. It is the router that can route traffic out of the local network. The gateway is the computer that routes traffic from a workstation to the outside network that is serving up the Web pages. A default gateway is the node in a computer network using the Internet Protocol Suite that serves as the forwarding host to other networks when no other route specification matches the destination IP address of a packet.
If you use the analogy that a network is like a room, then the default gateway is like a doorway. If you want to get to another room or network you need to find the doorway. The default gateway is used as the destination of all traffic that is not on the same subnet. The gateway is a layer 3 device such as a router or multi-layer switch that is used to route traffic on a hop-by-hop basis.
Alternatively, a PC or computer that does not know the IP address of the default gateway is like a person, in a room, that does not know where the doorway is. They can talk to other people in the room or network, but if they do not know the default gateway address, or there is no default gateway, then there is no way out.
A gateway is a node (router) in a computer network, a key stopping point for data on its way to or from other networks. The gateway address (or default gateway) is a router interface connected to the local network that sends packets out of the local network.