USB, short for Universal Serial Bus, is a standard type of connection for many different kinds of devices. Generally, USB refers to the types of cables and connectors used to connect these many types of external devices to computers.It is divided into three types according to the connection way and physical shape of the USB port and plug.
Also known as USB standard A connector, the USB A connector is primarily be used on host controllers in computers and hubs. USB-A socket is designed to provide a "downstream" connection intended for host controllers and hubs, rarely implemented as an "upstream" connector on a peripheral device. You can connect various devices such as smartphones, cameras, keyboards, and more to computers to transfer data, or plug into wall chargers to charge these gadgets with a Type-A port.
USB Type B connectors, officially referred to as Standard-B connectors, are square in shape with either a slight rounding or large square protrusion on the top, depending on the USB version. USB Type-B connectors are supported in every USB version, including USB 3.0, USB 2.0, and USB 1.1. This connector is designed to carry data and power in USB SuperSpeed applications. Cables with this connector are not backwards compatible with USB 2.0 or USB 1.1 devices; however USB 3.0 devices with this connection type can accept previous USB 2.0 and 1.1 cabling.
Micro USB is a miniaturized version of the Universal Serial Bus (USB) interface developed for connecting compact and mobile devices such as smartphones, Mp3 players, GPS devices, photo printers and digital cameras. Like standard USB, the micro versions are plug-and-play and hot-swappable.