Tohru is a term that likely originates from the Japanese name "直樹" or "Tōru." In the context of pornography, it refers to content involving a performer named Tohru or featuring Japanese elements. The term may also be used as a search query to find videos with such content. As this is a proper noun and not a general tag description, there isn't much further meaning beyond identifying the individual or theme involved.
It should be noted that "Tohru" can be written in various ways depending on context and writing system (Hiragana, Katakana, Romaji). Common spellings include とおる, トオル, or Tohru-kun. The character itself translates to something along the lines of "straight tree" or "honest wood."