What the anime is based on! Mostly of academic interest, but a useful bit of info.
Based on an interactive (even if minimally so) form of entertainment software, generally available for PCs, consoles, or arcade machines.
Any game where reflexes are the key to the gameplay, violence is optional.
Any game that contains (or had a version than contains) adult content (generally sex scenes), regardless of how the fanbois whine about how it's 'the story that matters'.
Manga is the lifeblood that drives the anime industry. Everything and it's mother is based on manga.
|However!||Be very sure the manga actually was the basis for the anime!|
Not only are manga adaptations of many popular anime made, there's a manga based on Evangelion and two (one shounen and one shoujo) based on each of Escaflowne and Mahou Tsukai Tai, but also it's quite common to release manga and anime versions of a story in parallel, for instance Nadesico and Shoujo Kakumei Utena.
Based on a live action film, Japanese or otherwise. For instance, Iria: Zeiram the Animation which is based, unsurprisingly, on the sf action film Zeiram.
Not based on anything, the story is a new work, usually made up by the people involved in creating the anime. Generally if an original work (原作) credit is given, it will be to the studio, or director, or other members of the production team.
Note that novel means book with words in paper, so no comics and no 'visual novels', which should go under manga and (probably h) game respectively. Examples include the many World Masterpiece Theatre series animated by Nippon Animation (日本アニメーション), the various anime based on the novels of Tanaka Yoshiki (田中芳樹) and lots of others.