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.