CLI stands for Command Line Interface. A CLI is a tool that you use to communicate with your computer, like giving it commands or retrieving data.
Many software frameworks and libraries, such as React and Angular, have a built-in CLI tool that allows you to quickly get a project up and running on a server on your local machine (localhost) by executing a few command lines.
Whenever you start working on a new app or website, there are usually some common UI elements, functionality, and project configuration that there’s no reason to custom code from scratch. With a well-equipped CLI, you can quickly bootstrap/configure your project with conventual design patterns and save you a lot of time that you can instead spend on building your product.