What is USB OTG ?
In simple layman’s terms, USB OTG is just that thing that enables you to connect to different USB devices from your Mobile/Tablet just as you use USB devices with your PC/Mac. Yes, and that means an USB OTG would allow you to connect an USB keyboard, or a Mouse or a PenDrive or a Hard Drive or even a Joystick, Printer or a scanner to your Mobile/Tablet powered by Android.
No Kidding!!! Next time, you could just play that Temple Run of yours and score way more than your peers after connecting your USB joystick to your phone.
Using some technical jargons, I would say:
The standard USB cable that you plug into your mobile device to connect to your PC/Mac uses a master/slave architecture i.e. your mobile or tablet works like a protocol slave and the Computer works as the Master. The computer can only start a communication to your smartphone. USB OTG or USB On-The-Go enables the
device to work as a master as well as the slave.
The device connected to the “A” end of the cable at start-up (known as the A-device) acts as the default host, while the “B” end acts as the default peripheral (known as the B-device).