The "ls" command is used in Unix-based operating systems to list the contents of a directory. When executed, ls lists file names, directories and subdirectories present in the current working directory by default. The command also provides a variety of additional options that allow users to modify the output to show extra information such as file permissions, modification date, and file size or to display the contents of specified directories apart from the current one. The ls command uses color codes in the output by default, which helps to distinguish file types and their permissions using different colors. This command is frequently used by developers and system administrators to navigate through the file system of Unix-based operating systems.