Man page is short for manual page, which is a type of electronic or software documentation usually found in Unix and Unix-like operating systems. It provides users with detailed documentation for included software programs, system commands, formal standards and conventions, and operating system nuances such as system and library calls. The man page is usually invoked through the command "man," followed by the object, command name or topic, e.g., "man shell."
Techopedia explains Man Page
Man pages are descriptive help systems that may also contain procedural help (such as how-tos) and, sometimes, even contain the history of the command, such as why it came to be and descriptions of its versions and revisions.
The first man pages were written in 1971 by Dennis Ritchie and Ken Thompson at the insistence of their manager Doug McIlroy. The Programmer's Manual was also created along with the man pages; this contained short papers and tutorials for general Unix usage, a manual for the C programming language, as well as documentations for the tools and applications such as Yacc.
Man pages are formatted by default using the troff typesetting package, either with the macro package, which is appearance oriented, or with mdoc, which is semantic oriented. This format makes it easy to typeset the man pages into Postscript, PDF or other formats for printing or viewing. A number of manual pages, especially those for applications, are now available in HTML, and most Unix systems even provide the man2html command package, which allows users to view the man pages using an HTML browser.
This definition was written in the context of Unix