When an illustration indicates who tops, and who bottoms in a relationship. Alternately, the illustration may contain multiple views of the same character annotated as being "top" and "bottom" versions of them.
Depending on context, that means either who's the one penetrating and penetrated, the one who dominates and the one who submits, the one who is active and who is passive, and so on. This also applies to other related terms, such as seme (攻め) and uke (受け), tachi (タチ) and neko (ネコ), or 凸 and 凹.
This practice is especially common in yaoi works that do not depict penetrative sex directly, as top/bottom preference in a character is often associated with specific personality traits, though it may also be seen in non-yaoi works.
