Kaiju Films are movies in which kaiju have appeared.
What Is A Kaiju Film?
Grossly oversimplifying it, a kaiju movie is a giant monster movie whose producers/creators say is a kaiju film. Kaiju is a Japanese word literally meaning "strange beast," but is usually translated as "monster," which is its English equivalent.
Generally speaking, a kaiju film is any film that is made in the East (Japan and other Asian countries) that is about (a) kaiju(s). However, not all kaiju films are made in the East. For example, Gorgo and Pacific Rim are considered kaiju films although they were not made in Asia.
There is no truly all-encompassing way to define a kaiju film or determine what films do or don't qualify as a kaiju film. In Japan, any film featuring a monster is considered a kaiju film, since kaiju is the Japanese term for a monster, so from a technical standpoint virtually any monster film is a kaiju film. But generally speaking, movies that make use of tokusatsu techniques to portray monsters or that feature well-known kaiju such as Godzilla, Gamera, and King Kong are considered kaiju films.