Bisexuality: Definition

Bisexuality is a sexual orientation which refers to the romantic and/or sexual attraction of individuals to others of both genders (socially) or sexes (biologically). Bisexuals are not necessarily equally attracted to men and women and may even shift between states of finding either gender or sex exclusively attractive over the course of time. However, some bisexuals are and remain fairly static in their level of attraction throughout their adult life.

Bisexual people are not necessarily attracted equally to both sexes. Because bisexuality is often an ambiguous position between homosexuality and heterosexuality, those who identify, or are identified, as bisexuals form a heterogeneous group.

source: http://en.wikipedia.org/wiki/Bisexuality