Ai network

It is created every map load and is a vital entity to all NPC functions. If you were to Kill it in the game, NPCs would freeze up entirely - no speech, no animations, no movement. Killing would also render all  console commands unusable. Generally, just don't touch this entity.

It is referred to as BigNet by the engine. Valve at one point intended to expand on this entity by making multiple of these work together in maps (this task can now be done with hint groups though).