A minigame (sometimes called a subgame or microgame) is a short video game often contained within another video game. A minigame is always smaller or more simplistic than the game in which it is contained. Minigames are sometimes also offered separately for free to promote the main game.
This theme is NOT intended for boxsets where multiple previously-separate games are bundled together in one box (aka a Compilation).
The Minigame Compilation theme is for single games which have multiple distinct subgames internally. So, Mario Party would qualify, but The Orange Box would not.