The Crystal PnP (Plug and Play) Windows driver typically refers to a software package that enables Windows operating systems to communicate with Crystal Semiconductor devices, such as audio or video hardware. Crystal Semiconductor, a company acquired by Cirrus Logic, was known for producing sound cards, audio chips, and multimedia devices that used their proprietary hardware. The Crystal PnP driver is used primarily for older Crystal sound cards or audio chips, allowing them to work with modern versions of Windows.