Class = prefab Object instance = instance created from the prefab https://qiita.com/nmxi/items/7950fb12ef925efa276d#4%E3%83%9C%E3%83%BC%E3%83%AB%E3%82%92%E5%8B%95%E3%81%8B%E3%81%99
The object instances created from a script need their own GameObject as a container to put inside.