Hello Marit
A default route is the route that is used to route packets when there is no specific match to any other route in the routing table. This is also known as the gateway of last resort. It is defined by using the 0.0.0.0 0.0.0.0 designation which essentially matches any IPv4 address.
Now a default route can be statically assigned simply using the command:
ip route 0.0.0.0 0.0.0.0 X.Y.Z.A
where X.Y.Z.A is the IP address of the next hop used for the gateway of last resort. However, a default route can also be learned dynamically via a routing protocol. You can configure a router to share it’s own default route (whether statically defined or dynamically learned) with other routers using a routing protocol.
For OSPF or RIP, this is done using the default-information originate command in the router configuration. For EIGRP you have some additional options which are further described in the EIGRP Default network Route lesson.
I hope this has been helpful!
Laz