Boi is a colloquial term for either a submissive biological female who dresses and behaves in a masculine or butch manner, or an effeminate man. The first sense of the term is most commonly used in lesbian D/S relationships, but not exclusively in this context.
A boi may be male or female, transsexual, transgender, or intersex. A person typically adopts the term as they struggle to identify with more mainstream gender labels. No matter what the person’s gender or sexual orientation, a boi tends to be young and boyish or adolescent in appearance.
The term boi was originally coined in the black LGBTQ community, but its use has now spread throughout mainstream society.