BDC may refer to any of the following:
1. Short for Backup Domain Controller, BDC is a backup computer in a Microsoft Windows NT 4 network that has a duplication of the user accounts on that network. These backup accounts are never written to, only read from to help keep the data protected. The BDC has been replaced by Windows 2000's Active directory.
2. Chat slang for big dot com, or big dumb company.