Plug and Play, sometimes, abbreviated PnP, is a catchy phrase used to describe devices that work with a computer system as soon as they are connected. The user does not have to manually install drivers for the device or even tell the computer that a new device has been added. Instead the computer automatically recognizes the device, loads new drivers for the hardware if needed, and begins to work with the newly connected device.
For example, if you connect a Plug-and-Play mouse to the USB port on your computer, it will begin to work within a few seconds of being plugged in. A non plug-and-play device would require you to go through several steps of installing drivers and setting up the device before it would work.
While Plug and Play usually refers to computer peripheral devices, such as keyboards and mice, it can also be used to describe internal hardware. For example, a video card or hard drive may be a Plug and Play device, meaning the computer will recognize it as soon as it is installed. The only difference is that internal components usually require the computer to be turned off when they are installed, while external devices can typically be installed while the computer is running.