A USB-based adapter for Ethernet, Bluetooth or some other wireless technology. Functioning as the base station's transmitter/receiver (transceiver), the USB plug is attached to the unit, which extends out from the USB socket.
A Wireless Mouse Dongle
This Logitech unit is a dongle for a wireless mouse. When not in use, this dongle conveniently snaps to the underside of the mouse for travel and turns the mouse off at the same time. When released from the mouse, it turns the mouse on.