A universal serial bus, or USB, device refers to any device that utilizes USB connections to connect to a computer. Common examples include external hard drives, webcams, printers, scanners, digital cameras, keyboards and mice. The USB connection symbol is usually denoted on the connector.
There are some USB devices that require a USB cable to be connected to them before they are plugged into the USB port of a computer. Other devices like keyboards and mice have a permanently attached USB cable, and some devices like flash drives have a built-in USB connector.
USB devices can be connected and disconnected from a computer easily without restarting it because most are "plug and play." When the USB device is connected, the computer automatically identifies and installs the required drivers. If the driver is not available, the device will not work properly.
Unlike most of the other data cables, such as HDMI or Ethernet, the ends of USB cables have different types of connectors, such as a B-type or an A-type. USB cables and ports also vary in size, particularly on the B connector end. The "standard" size is used on USB flash drives, the "mini" size is widely used on digital cameras and the "micro" size is used on modern smartphones.