localhost

Category: Where you actually do the work

localhost — A special address that always means "this computer." When you open localhost in a browser, you're talking to a program running on your own machine.

Why you care

Almost every web app you build locally shows up at something like localhost:3000. It's how you test things in a browser before anyone else can see them.

When you hear it

"Open localhost:3000." "It works on localhost but not in production."