What is "BC 1.2 port"?
Battery Charging spec
BC 1.2 is an abbreviation for (USB) Battery Charging (revision) 1.2. I'm no USB specs specialist so I can link some abstracts/files only:

USB Battery Charging (Wikipedia)
USB Battery Charging Revision 1.2 (PDF)
Overview of USB Battery Charging Revision 1.2 and the Important Role of Adapter Emulators
Overview of USB Battery Charging Revision 1.2 and the Important Role of Charger Detectors

Basically it's a USB 3.0 port with some extra features to detect devices that can make use of charge currents beyond the standard 900mA.