Originally Posted by firstname.lastname@example.org
Please tell me what is 4 in the output of this command
It gives the number of links to that item. In the case of a file, this will be the number of hard links, typically one, where it is only in a single location. In the case of a directory, it will typically be the number of subdirectories plus 2 (ie, the link from the directory above, the '.' link from itself, and the '..' links from the subdirectories).
You can get more detailed documentation by typing 'info ls'.