Smartphones have the capability that: 1. You can plug them into your PC and they act as a device (e.g. mass storage device for downloading your photos, drawing

Smartphones have the capability that: 1. You can plug them into your PC and they act as a device (e.g. mass storage device for downloading your photos, drawing power to charge) 2. You can plug devices into them, and they'll act as a host (e.g. you can plug in a mouse if your touchscreen is broken, download the photos from your non-smartphone camera onto your smartphone, supply power to charge something else) 3. They'll do all this through a single port. Hardly any normal people use these capabilities, as the cables are somewhat rare and the software support is somewhat patchy. But if you're buying a development board ready to make your own product, you can read this as "can be a usb host or device, whichever your product needs"