Threat Vector: the attackable landscape available to the threat agent/actor.
A task of the security specialist is to decrease the threat available realestate (landscape) for the threat agent/actor to attack. If you have ten doors in your house you want to consolidate it down to one door.
In the below on the (LEFT) we have the current state where we have a bunch of public IP addresses spread across the network that are advertising services. These are spread across a vast horizontal distance (threat landscape) that enables the threat actor to attack.
The solution to the below problem is to (RIGHT) consolidate the IP ranges under a set of technologies that we can put protection against and really focus on securing.