Anime Type

Anime types represent the medium for which an anime was first released.

unknown

Anime that has no type set yet. Generally for anime that hasn't been released yet.

TV Series

Anime that is first released as a series on TV.

OVA

Original Video Animations (OVA) are animated films and series made specially for release in home-video formats (e.g. VHS, DVD, BluRay).

Original Animation Discs (OAD) are animated films and series made specially for release as an item bundled with something else, such as a manga, light novel, visual novel, etc.

Movie

Anime that is first released as a movie in theatres.

Other

Anime that doesn't fall into any other category.

Web

Anime that is first released as streaming media.

Original Net Animations (ONA) fall into the Web category, rather than the OVA category as the name may otherwise suggest.

TV Special

Anime that is first released as a one-off, (generally) non-recurring episode/movie on TV. A TV special can have multiple episodes.
A notable differentiation from a normal TV series is that TV specials generally are not serialized. Further, if Japan/China/Korea specifies that it is a TV special, it is probably a TV special.

Music Video

Anime that is a music video.