Default Gateway
The device (usually your router) that traffic is sent to when leaving the local network.
Every device needs to know its gateway to reach the internet. On a home network it's typically an address like 192.168.1.1.
Related articles
IP Address
A numeric label that identifies a device on a network, such as 192.168.1.10 (IPv4).
Subnet
A logical subdivision of an IP network, defined by a mask that separates the network and host portions of an address.
NAT(Network Address Translation)
The router technique that lets many private devices share one public IP address.