How to hide and show level based on player/camera position?

I don't actually know what this is called in Unity terms so the best I can do is provide an image and explain.

Basically, the camera follows the player as they move around. The visible part of the level is a fixed size, but hides and reveals hidden parts of the level as the player moves (which in turn causes the camera to move). I would like to do this in 3D.

I have a 3D scene set up with a simple plane for a floor and a capsule collider for my player. Eventually, there will be other npc's and level geometry that will all be affected but the hiding and showing effect. Basically, the intended effect is to only ever show what is within the player's immediate area and obscure the rest in shadow.

I'm very sorry that I don't know what this effect is called or know better specifics to look into online. Thank you for any help!