Command language is a way of talking to a computer in a way that it can understand. It's kind of like you telling your friend what to do - but instead of using words, you use specific commands that the computer recognizes.
So let's pretend you want to ask the computer to open up a file for you. Instead of saying "Hey computer, could you please open up this file for me?" you would use a command language, which might look something like "open file-name.txt." The computer would recognize this command and do what you asked it to do.
Command languages are often used by programmers and people who work with computers a lot, because it can be a really fast and efficient way to get things done. But just like learning any new language, it can take some practice to get the hang of it.