Topic is one of the core types in Freebase. Topics contain a set of default properties that are generally useful when describing a topic: display name, alias, article, image and webpage.
Most types in Freebase carry these topic properties by default. If an item in Freebase is typed 'topic' it will show up in search results. You will never see 'topic' as one of the available views, however as its properties are embedded in and shared with the other types applied to an item in Freebase.
This all may seem kind of abstract, but we do this in order to make it easy to share these common properties across types -- so you don't end up with a bunch of different articles about the same thing.