SubSurf works as long as it’s quads. There are different kinds of poles in quad topology. Nose Pole or N-Pole for short is 3 edges connected to a vertex. This is common when modeling a characters nose. Thus why it’s called a nose pole. In your case it’s an Extrude Pole or E-Pole for short. These are common when you extrude. They also control the flow of face loops. In this case(Second image) you have 2 triangles that are small and thus stops the pinching caused from the SubSurf modifier. Since they are small The affect on the shading is very small. I hope that makes sense. Also there is the 6+ Pole with is as you guessed is 6 or more edges. you can see this in the top and bottom of the UV Sphere. This is also called a Fan topology.
