Where to get these nodes that don't appear in the search menu? I am a beginner and am trying to replicate node groups I see in images.

Forgive me if this is a stupid question to you, but I can't seem to find certain nodes. 

For example, I see the IOR node in someone's setup,



but I can't seem to find it when I search for it.



Does anyone know how I can get these "hidden" nodes?

EDIT: This is NOT a duplicate. The duplicate mentioned is talking about nodes in the compositor, while these are actual nodes in the material node editor.
IOR is just a regular numeric value, there is no specific node for it.

What you see in that image is just a renamed node title, the actual node type is a simple Value. You can change the label of any node from the sidebar.

Just select a node, expand it with the N key and change the Label field.