The ISDN Adapter (PCI Bus W) driver refers to a driver for an ISDN (Integrated Services Digital Network) adapter installed on a computer via a PCI (Peripheral Component Interconnect) bus. ISDN is a set of communication standards for digital transmission of voice, data, and video over traditional telephone lines. In the context of computer hardware, an ISDN adapter allows a computer to connect to an ISDN network for high-speed data transfer, voice calls, and fax services.

The "PCI Bus W" suggests that this adapter is using the PCI bus to interface with your computer's motherboard, and the "W" may refer to Windows (indicating a Windows driver).