Universal Serial Bus (USB) is an industry standard that was created in the mid 1990s for connecting computers to peripherals. Before USB, devices were connected to computers by RS232 ports and parallel ports. USB can be used for more than just creating a communication link between two devices, it can also be used for charging/powering devices.
USB has gone through many changes over the years. Starting with USB 1.0: it was capable of transferring data between 1.5Mbs to 12Mbs. Transferred speed for USB 2.0 was increased to 480Mbs, and then again to 5Gbs for USB 3.0.
Connectors for USB normally come in two types: Type A and Type B. Type A connectors are mostly found on computers and power adapters. Type B connectors are smaller than Type A connectors, and are mostly found on smaller devices (peripherals). A USB cable normally has a Type A connector at one end, and a Type B (mini) connector at the other end.