man (short for "manual") pages are the Unix/Linux way of documenting things.
This is a mirror of the ones that apply to file formats.
|1||User commands that may be started by everyone.|
|2||System calls, that is, functions provided by the kernel.|
|3||Subroutines, that is, library functions.|
|4||Devices, that is, special files in the /dev directory.|
|5||File format descriptions, e.g. /etc/passwd.|
|7||Miscellaneous, e.g. macro packages, conventions.|
|8||System administration tools that only root can execute.|
|9||Another (Linux specific) place for kernel routine documentation.|
|n||(Deprecated) New documentation, that may be moved to a more appropriate section.|
|o||(Deprecated) Old documentation, that may be kept for a grace period.|
|l||(Deprecated) Local documentation referring to this particular system.|
manpages, from Harvey Mudd College.