This is where any files and folders that aren't scans or metadata but are related to the collection go. Common files for this folder include
- Thumbs icons - thumbnail-size icons for use in presenting the collection online.
- Collection XML file -- or if this is a "combo" set of mini-collections, a comboColl.txt, which then results in multiple collection XML files after preparation for upload.
Try to limit yourself to keeping only vitally necessary files in the Admin folder, and as much as possible convert them to .txt or .xml.