The term "hentai-sub" refers to a type of adult animation content that falls under the Japanese genre known as "hentai." It typically features explicit and sometimes grotesque sexual situations, often with fantastical or supernatural elements. The "-sub" portion of the term indicates that this is a subtitled version of such content, meant for audiences who prefer to read the dialogue in their own language rather than watching a dubbed or localized version. In essence, "hentai-sub" describes an adult animated video with explicit sexual content, presented in its original language form with English subtitles.