USB-A and 2.4 GHz receivers

What it is, physically

The familiar rectangular USB socket, and the small dongle that lives in it. A 2.4 GHz receiver is a radio on a stick: it occupies the port for as long as the device is in use, and it is not shared between devices unless a manufacturer says its receiver is shared.

What can be inside the same shell

• A receiver paired to one specific device at the factory.
• A receiver a manufacturer states will serve several of its own devices.
• A wired device, which occupies the same port with no radio involved.
• Anything else you were going to plug in, which now has one fewer place to go.

Who decides, and where it is published

The USB Implementers Forum publishes the USB specifications. The 2.4 GHz link between a receiver and its device is the manufacturer’s own, and is not a published interoperable standard the way a Bluetooth pairing is.

Reading a listing that uses this word

Count them. That is the whole technique. Every device in a setup that states a receiver, plus every device that states a cable, is one port, and the total is compared against the ports on the machine. The Port Budget tool on this site does the addition and refuses to guess at the second half, because no listing here states how many ports a machine has.