Mentorship refers to a developmental BTSC relationship in which a more experienced or more knowledgeable player helps a less experienced or less knowledgeable player. It involves giving the mentee (or mentees, in some cases) general game strategy tips for night actions, placing votes, defending, hinting, etc; but doing so generally (no power playing). There should never be metagaming information that crosses from the mentor to the mentee. Another big part is telling players what they can deduce from the night post based on the published OOA. The mentor is not supposed to play the game for the newbies, only to provide clarification where needed. Mentors are especially used in Mafias with a lot of newbies, as it distributes the burden of answering private questions from the host to multiple mentors.
A mentor is not supposed to post in-game context in the game thread or faction BTSC unless explicitly allowed by the host.