A type of USB connector. USB stands for "Universal Serial Bus". Devices connected to the computer using a USB cable can easily exchange files and information (if the device supports Mass Storage mode, the files can be transferred without the need for special drivers or software).
Some devices can be charged via the USB cable when connected to the computer. There are different USB interfaces: MicroUSB (with two subtypes - Micro-A and Micro-B) is one of them, and was developed to replace the older MiniUSB interface. However, the latter is still the most popular connector type in portable devices.