"Download QC" is a QC mode where assets are downloaded locally for QC (differing from Cast QC, or Browser QC where assets are streamed on Asset QC) and it's a method of performing QC currently employed for reviewing IMFs, Print Masters, M&Es and ATMOS files.
Download QC is the highest tier QC, where the full IMF is downloaded from Backlot and QC’d in a bay using scopes, high-end monitors, and an appropriate audio environment for the audio supplied.
The purpose of this tier is to be the most in-depth because it allows the use of more sophisticated equipment and tools to complete a QC task. Download QC often finds quality errors in higher quantities. This can be useful when post production is prepared to make as many fixes as needed.