The Jargon File (version 4.4.7, 29 Dec 2003):

man page
 n.

    A page from the Unix Programmer's Manual, documenting one of Unix's many
    commands, system calls, library subroutines, device driver interfaces, file
    formats, games, macro packages, or maintenance utilities. By extension, the
    term ?man page? may be used to refer to documentation of any kind, under
    any system, though it is most likely to be confined to short on-line
    references.

    As mentioned in Chapter 11, Other Lexicon Conventions, there is a standard
    syntax for referring to man page entries: the phrase ?foo(n)? refers to the
    page for ?foo? in chapter n of the manual, where chapter 1 is user
    commands, chapter 2 is system calls, etc.

    The man page format is beloved, or berated, for having the same sort of
    pithy utility as the rest of Unix. Man pages tend to be written as very
    compact, concise descriptions which are complete but not forgiving of the
    lazy or careless reader. Their stylized format does a good job of
    summarizing the essentials: invocation syntax, options, basic
    functionality. While such a concise reference is perfect for the
    do-one-thing-and-do-it-well tools which are favored by the Unix philosophy,
    it admittedly breaks down when applied to a command which is itself a major
    subsystem.


The Free On-line Dictionary of Computing (30 December 2018):

Unix manual page
man
man page
Unix man page

    (Or "man page") A part of Unix's
   extensive on-line documentation.  To read a manual page from
   the Unix command line, type:

   	man [-s
] 

   e.g. "man ftp" (the section number can usually be omitted).
   Pages are traditionally referred to using the notation
   "page(section)", e.g. ftp(1).

   Under SunOS (which is fairly typical), Section 1 covers
   commands, 2 system calls, 3 C library routines, 4 devices
   and networks, 5 file formats, 6 games and demos, 7
   miscellaneous, 8 system administration.  Each section has an
   introduction which can be obtained with, e.g., "man 2 intro".

   Manual pages are stored as nroff source files.  Formatted
   versions are also usually cached.  Man pages for most versions
   of Unix are available on-line in HTML.

   Unix manual page: man(1).

   Linux man pages (http://www.kernel.org/doc/man-pages/).

   Solaris man pages (http://docs.sun.com/app/docs/coll/40.10).

   (2010-01-19)