default gateway
The router a device sends a packet to whenever the destination isn't on its own subnet.
The default gateway is the router address a host uses for every destination outside its own subnet.
Examples
The sensor at 192.168.1.37/24 sends a packet for 198.51.100.7 to its default gateway 192.168.1.1, because that address isn't on its subnet.
A packet for the laptop at 192.168.1.10 goes directly, with no default gateway, since the laptop shares the sensor's /24.