It is not a new term at all, in fact it dates back to the early days of role-playing and is widely attested in the publication of many classic games, such as Dungeons & Dragons, but not only. Here is a roundup of examples.
Old School games have a definite time frame. Adventure Games may refer to any game that follows the principles contained in the Manifesto. Even if it is written today.
Furthermore, Adventure Games does not necessarily refer to a rules framework descended from D&D. Any rule system can power an Adventure Game if it respects its design and game principles.
OSR is an umbrella acronym that refers both to Old School games in the strict sense and to their retroclones, going from merely compatible games to games that are related in spirit but not in mechanics.
In addition, OSR has developed for nearly two decades to cover both a design movement and a constellation of communities. It has also become a commercial label.
Adventure Game is neither a commercial label nor a community. It is a set of design and game principles that also apply to OSR games, but not necessarily.
Quite the opposite! Adventure Game is neither a commercial label nor a community. It is a set of design and game principles that also apply to OSR games, but not exclusively necessarily.
It is cross-sectional and wants to unite, not divide!