What kind of node is this?
Image from this blog post
Blender Stack Exchange is a question and answer site for people who use Blender to create 3D graphics, animations, or games. It only takes a minute to sign up.Sign up to join this community
Each important in and output of a group of nodes can be wired to the group in- and output nodes to make them accessible when the group is collapsed.
The new style looks like:
Single Node nonsense example
You can collapse the view of a node group using the up-arrow button from the menu header, and expand it by clicking the icon right to the nodes title.