What is unallocated $orphan file data ?

Good morning! I've been learning a lot about digital forensics lately. I made a little test case for myself using VMs and I have a question that I cannot find the answer to.

I did an ingest and analysis for a disk using Autopsy.

I did a keyword search for a suspect IP of a C2 server. I got many hits in autopsy.

One of them is the name OUTLMIME.DLL and it's location is in img\_c:/$OrphanFiles/OUTLMIME.DLL; this shows as unallocated. …

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