What is a default gateway? What happens if I don't have one? Linux

What is a default gateway? What happens if I don't have one?
a gateway is a routing device that knows how to pass traffic between different subnets and
networks. A computer will know some routes (a route is the address of each node a packet
must go through on the Internet to reach a specific destination), but not the routes to every
address on the Internet. It won't even know all the routes on the nearest subnets. A gateway
will not have this information either, but will at least know the addresses of other gateways it
can hand the traffic off to. Your default gateway is on the same subnet as your computer, and
is the gateway your computer relies on when it doesn't know how to route traffic.
The default gateway is typically very similar to your IP address, in that many of the numbers
may be the same. However, the default gateway is not your IP address. To see what default
gateway you are using, follow the steps below for your operating system.