command line
A text window where you type commands instead of clicking buttons, used to run tools and scripts for your project.
Like walking up to a service counter and stating exactly what you need. The command line is a window where you type a command, the computer runs it, and prints the result. People also call it a terminal or a shell, which are programs that show this window.
It matters because many developer tools only live here: installing packages, starting Expo, checking code, and saving changes. A package is a bundle of reusable code, and a script is a saved command you can run again.
In practice you open the project folder, run a command to start the app, another to install a library, and another to make a commit. Small typos break commands, so copy carefully and stay in the right folder.