That number refers to the section of the man pages that the command is in. See http://en.wikipedia.org/wiki/Man_page#Manual_sections http://en.wikipedia.org/wik

That number refers to the section of the man pages that the command is in. See http://en.wikipedia.org/wiki/Man_page#Manual_sections http://en.wikipedia.org/wiki/Man_page#Manual_sections for an example list; however, it seems the list is not the same between systems.