A Computer That Serves
The word "server" sounds specialized, but at heart a server is just a computer. What makes it a server is its role rather than its shape. While the computer or phone in your hands is built to be used directly by one person, a server sits somewhere on a network and spends its time answering requests from other computers, handing out information or running services on their behalf. The name comes straight from this job: it serves.
Client and Server
Most of what you do online follows a simple pattern called the client–server model. Your device is the client: it asks for something. The server is the machine that receives the request and responds. When you open a web page, your browser, the client, sends a request to the server that holds that page, and the server sends the page back. The same back-and-forth happens when you check email, watch a video, or save a file online. One side asks, the other serves.
What Servers Do
Different servers are set up for different tasks. A web server stores and delivers websites. A mail server handles sending and receiving email. A file server keeps files so people can reach them from many devices, and a game server coordinates an online match between players. A single powerful server can handle requests from a great many clients at once, which is how one website can serve millions of visitors.
Where Servers Live
Because servers need to be available at all times, they are usually not kept in homes. They are gathered in large, specially built buildings called data centers, where they run around the clock with reliable power, fast internet, and cooling to manage the heat of so many machines. When people talk about storing files or running things "in the cloud," they are really talking about servers like these, working away in data centers somewhere, ready to serve whenever a request comes in.
Source
This article was written using information from Wikipedia.