PUM stands for Potentially Unwanted Modification. These are modifications made from their default settings in Windows.
Some PUM examples would be ForceClassicControlPanel or NoViewContextMenu.
In a business environment it is not uncommon for these changes to be a part of your Group Policy. Before removing PUMs, please check to see if these changes are a part of your policies. If they are, you can add these to your ignore list.
Since these detections are per user, you will need to use a wildcard in the registry entry to make sure it is ignored on all systems in a policy.
Using one of the examples from before, it may show up as:
The long section starting with S is the SID. We'll replace this with an asterisk:
This will now properly ignore the entry for all users and all computers using the policy this was entered into.