Bisexual (often shortened to Bi) refers to someone who is attracted to multiple genders, from a range of 2 to all genders, with or without preference. It is also sometimes defined as the attraction to genders both the same as and different to one's own. This does not necessarily refer to one only being attracted to binary genders (males/boys/men and females/girls/women), as some think: the bisexual community has an extensive history of challenging the gender binary, and bisexual activists have been outspoken about this fact.

Bisexuality encompasses a wide spectrum of attraction. A bisexual may be attracted to any number of genders, from two to all, and may be attracted to any genders in any combination (including non-binary genders). Bisexuals may or may not have a preference and may or may not feel a difference between their attraction to different genders.

Bisexuality can be similar to pansexuality and other multisexual identities. The differences between these identities usually comes down to individual preference, particularly where some may feel that different terms communicate their personal experience of attraction with more accuracy. Each bisexual individual may choose to define their attraction slightly differently.

The romantic counterpart is biromantic.