top/bottom dynamic annotated
When an illustration notes who tops (is the one penetrating), and who bottoms (is the one penetrated) in a relationship. This also applies to other related terms, such as seme (攻め) and uke (受け).
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.