The primary function of an Ethernet cable is to provide a wired connection for transmitting data between devices in a local area network (LAN). It enables reliable, high-speed communication by transmitting electrical signals over twisted pairs of copper wire. Ethernet cables are essential for connecting computers, routers, switches, and other network devices to ensure stable internet access and efficient data transfer. The use of Ethernet cables supports various standards, such as Fast Ethernet and Gigabit Ethernet, allowing for faster and more efficient networking.