This tutorial explains the difference between default route and default gateway.
A default route is a route entry in a routing table whereas a default gateway is a value, typically an IP address. When an IP packet is received by a router, it looks into the destination IP address in the packet. It then checks in its routing table if it is aware of the network address corresponding to the IP packet. It would then forward the packet out on the required interface to which the network is connected. If the destination network is unknown, the packet would be dropped. What if the router is directly connected to another router, which knows about the destination network in the IP packet. In this scenario, two options can be configured. The default gateway of the first router can be configured with the IP address of the second router. When this configuration is performed, a route entry would be automatically populated in the routing table. This route entry is known as a default route. Instead of configuring the default gateway, a default route entry can also be configured directly on the router.