House organs come in two types, internal and external. An internal house organ is meant for consumption by the employees of the company as a channel of communication for the management. An external house organ is meant for consumption by the customers of the company, and may be either a free regular newsletter, or an actual commercial product in its own right.
A canonical example of a commercial house organ would be the Avalon Hill General, which had no outside advertising (usually a major portion of a magazine's budget). It featured news, strategy articles, variants, and essays on game design—all about Avalon Hill games. Until very late in its run, there was no mention of the game industry outside of Avalon Hill itself.
Management Magazine: House Organ With a `Spin'; OPM's Slick Quarterly, a Survivor of Publication Cutbacks, Reflects What's Right
Dec 02, 1987; More than a quarter of all government publications have bitten the dust since the Reagan administration took office, including...
Hawks at the Washington Post: The House Organ for America's Political Class Is Pushing Bush's Case for War. (Articles)
Nov 11, 2002; On August 27, Richard Holbrooke, in an article on the Washington Post's Op-Ed page, endorsed President Bush's policy of regime...