From Test-Scratch-Wiki

uploader is a usergroup which is allowed to upload files on the server into MediaWiki. Uploaders therefore can upload large files at a very fast rate, and of a big mass. However, the user must have FTP access. The usergroup on the Scratch Wiki is unused.

Use

To use this role, one must download the extension for it, located here. More information on how to download the extension can be found here.