The term "Asian" in the context of a porn video generally refers to content involving performers who are of Asian descent. This could include individuals from countries such as China, Japan, Korea, Thailand, or Vietnam, among others. As with any ethnicity-based tag, it's intended to help viewers find specific types of content they may be interested in.
"Asiants," as a potential misspelling or alternative form, could have a similar meaning and refer to Asian performers or themes within the video.