The Brother MFC-490CW Fax Only Windows driver is a software component that allows your computer to communicate with the Brother MFC-490CW all-in-one printer, specifically enabling the fax functionality. Although the MFC-490CW is a multifunction printer that also supports printing, scanning, and copying, when you refer to the "Fax Only" driver, you're likely referring to a driver setup that focuses on fax capabilities without enabling the other features, like printing or scanning.