BL, which stands for boys' love, is a category that encompasses relationships between men. Yaoi and shounen-ai both depict BL but in different degrees of intimacy. Instead of focusing on the physical side of the relationship such as with yaoi, shounen-ai focuses on the emotional end. This genre may even go so far as to include titles that reflect foundational aspects like that found between family members.
Source：https://www.cbr.com/shounen-ai-anime-series-melt-heart/
