A Microgame is a type of minigame in the WarioWare series that only lasts a few seconds. It was introduced in WarioWare, Inc.: Mega Microgame$!. In the WarioWare series, all microgames have a genre such as Crazy Cars being in the Introduction game section. There are also boss microgames. They are the same thing, except for being a tad bit harder and last longer than regular microgames and are found at the end of each series of microgames. Microgames also can be created in WarioWare: D.I.Y. Also, there are microgames in WarioWare: D.I.Y. Showcase and Game & Wario.
For a complete list of microgames, check Here