The primary purpose of a network interface card (NIC) is to provide a hardware interface between a computer and a network. This card enables devices to communicate over a network using protocols such as Ethernet or Wi-Fi. The NIC converts data from the computer into a format suitable for transmission over the network and vice versa. It also manages MAC addressing, allowing for the identification of devices on the network. Overall, a NIC is essential for enabling wired or wireless connectivity and facilitating data exchange among connected devices.