Bisexuality is sexual behavior or an orientation involving physical or romantic attraction to both males and females.

It is mostly used for men and woman, although sometimes it is also used for transgenders and pan-sexuality might be included. It is one of the three main classifications of sexual orientation, and it situated somewhere in between the heterosexual and homosexual orientation. Be it right in the middle or more towards the left or the right of the scale. People who have a distinct but not exclusive preference for one sex over the other may also identify themselves as bisexual.

Bisexuality has been observed in various human societies and elsewhere in the animal kingdom.

The term bisexuality, however, like the terms hetero- and homosexuality, was coined in the 19th century.