In computing, a server is a computer or computers that send data over a network. This data can be a website, a program or photo file, or even information about the weather for an app on your phone.
Servers listen for requests from clients, which are other computers or devices. When a server hears a request, it reads it and responds by sending data back to the client.
For example, when you enter freecodecamp.org in the address bar, our server hears the request from your browser. Our server reads what page you want and looks for all the data (HTML, CSS, JavaScript, and photos) for that page. Then when everything is ready, it sends that data back to your browser.
Almost any computer with the correct software can act as a server. But the servers behind many popular websites and services are often built with special hardware. This allows the servers to handle many requests at once, and stay online for long periods of time.