Calciphylaxis. Calciphylaxis is a condition characterised by necrosis (cellular death) of the skin and fatty tissue. It is seen mainly in patients with end stage kidney disease. It is also sometimes called calcific uraemic arteriolopathy.
Besides a data link, USB provides 5 +/- 0.25 volts to power an otherwise unpowered device or charge a battery in a self powered device. A USB controller or hub is required to power one unit load (100 mA, a low power load). It can optionally power up to 5 unit loads (500 mA, a high power load).
Some clarification: I have an external HDD that gets it power from the USB port. Even if I turn of the computer, the HDD won't shut down, because there's power-off charging on that port. This is my only USB3 port, so using an other port is not an option.