You can use this optional field to write a text description for people who cannot see the file. The description should be enough for them to understand the purpose and information given by the media item. This is vital for blind users and other people using screen-reader software or text-only browsers.
The database is currently locked to new entries and other modifications, probably for routine database maintenance, after which it will be back to normal.
The system administrator who locked it offered this explanation: Major Server Maintenance, Access wil be restored soon.