Network interface cards allow computers to connect to networks. They are needed to access the Internet and local networks, and they can function with custom networks types as well. Wireless cards are generally called wireless network interface cards.
In general, people refer to Ethernet-enabled cards are NICs. Wireless cards are sometimes called WNICs, but they are often just called wireless cards. However, the term "NIC" encompasses all of these items. While Ethernet ports and cards are less common than they once were, they are still important for enterprise infrastructure, and servers use them to control multiple connections and to handle a high volume of traffic.
One NIC can handle a number of Ethernet connections by attaching a switch or router to it. While most people are used to standalone routers, many enterprise and server-grade routers are full servers attached to switches. In some cases, two or more NICs might be used to provide more throughput.
Offices often use Ethernet connections for workstations and desktops. Ethernet cables are easier to configure than wireless cards, and they can provide better throughput in certain scenarios. As more offices move to cloud-based operations, Ethernet cables are likely to be used to prevent wireless channels from becoming congested.