What is a server?

A server is just a computer running specialized software. Unlike your laptop, a server usually isn't connected to a screen, it's just connected to the internet.

For example, a web server is just a computer running web server software like Apache or NGINX.

Servers usually live in what's called a "data center", which is just a fancy name for a building where you can put your server.

But during development, you can run the specialized server software on your laptop as well. And in that case, your laptop is technically the server.