Defining Node Groups I will appreciate for your help.
I am creating my material library, and trying to clean and rename all materials and nodegroups.
How i can define from outliner (or any enother way) wich materials use this nodegroups

(update)

Thank you for your help. I'll try to be more specific.
Just for example. I have big scene with 105 materials, Also I have unknown node group (x) which is used by 3 users. It means that 3 materials from all 105 use this node group (x) The question is, how i can easily find these 3 materials? Where this information is shown in outliner?

Thank you
Node Groups can be renamed either in the Properties of the Node Editor, or also in the Outliner by editing the 'Name' attribute:



(update)

How to find which are the users of some datablock (it doesn't matter if it is a material or group, the idea is the same):

The datablock itself does not store who the users are, instead you have to go over all the users and test.
See:
How to know which object is using a material
Display all users of a datablock