The command "mkdir" stands for "make directory" and is used in various operating systems, including Linux, macOS, and Windows. It allows users to create a new folder or directory in the file system, helping to organize files and data efficiently. To use "mkdir," you simply type the command followed by the desired name of the new directory. For example, entering "mkdir myFolder" will create a folder named "myFolder" in the current working directory. This command is essential for managing files and maintaining an organized structure on your computer.