Sentry nest 

A Sentry nest is a term used in the multiplayer online game: Team Fortress 2. The term refers to an area in which one or more players of the the Engineer class has set up their buildings, (primarily) the Sentry gun, Dispenser, and Teleporter in a way that it acts like a small base for their team to retreat to when they are in trouble. It is common behavior for the Engineer to "turtle" in the nest and not stray away from his buildings. This behavior can stem from a fear of enemies of the Spy class to place an Electro-Sapper on his buildings. These nests are commonly set up behind cover, with a corner for the Engineer to keep his back against to avoid being backstabbed by a Spy.

Player on Red Team: "Watch out, the Blu team has set up a Sentry nest over there."

Sentry nest by WingedBluJ June 28, 2017