Original: However, an extension to USB standard specification called USB On-The-Go (the capitalization oddity is deliberate) allows a single port to act as either a host or a device — chosen by which end of the cable plugs into the receptacle on the unit.
Simplified: However, an extension to USB called USB On-The-Go allows a single port to act as either a host or a device — chosen by which end of the cable plugs into the socket on the unit.