USB stand for Universal Serial Bus. Many of today's smart phones employ a USB cable to power the battery.
The world can thank seven different companies for the advent of the cord. These companies include Compaq, DEC, IBM, Intel, Microsoft, NEC and Nortel. The idea was to come up with a way for all their devices to be able to communicate. It helped their businesses. The consumer could buy a piece of hardware from one of these companies and buy another piece of hardware and connect them with a USB cable. It made buying from these seven companies convenient and it drove their sales up.
Not all cords are made the same. Some have different sizes and others have different capabilities. Most of the sizes are displayed right on the connector of the USB cable.