Bisexuality

The official bisexual flag. The flag was created in 1998!

Ah, bisexuality. There are are few definitions floating around the internet for bisexuality. Here are a few:

• anyone who is attracted romantically and/or sexually to more than one gender (https://biresource.org)
•  physical attraction, romantic attraction, or sexual behavior that is not limited to one sex.  (www.bi.org)
• characterized by sexual or romantic attraction to both men and women (Merriam-Webster)

It is a type of multisexual attraction (meaning sexually attracted to more than one identity). The exact difference between "bisexual vs polysexual vs pansexual/omnisexual" varies wildly from person to person. Linguistically, bisexual can be broken down to "two + sexual". HOWEVER, there are many ways to interpret this "two" ("my gender and others" is a commonly used example of this, which by its very nature includes a multitude of gender identities and/or sexes).

The bisexual flag was crafted in 1998. The flag was created by a team that was led by Michael Page. The color meanings (from viewer top to bottom, according to Page themselves): the pink references same-sex attraction, the purple references sexual attraction to both sexes and blue references sexual attraction to the opposite sex.  

The bisexuality community is vast. Many LGBTQIA members are advocated for unity between the multisexual communities (pansexual/omnisexual, polysexual, bisexual, etc.) because (as they put it) "senseless fighting only harms our community" (referencing the LGBTQIA community). 

Heteroflexible (elasexual) and homoflexible (anisosexual) depends on the individual for if they're seen as a sub-community of the bisexual community or separate identities altogether. The argument for them not being "biphobic" is (in their words) "I don't have anything against the bisexual community or bisexual people, I just don't feel comfortable associating with the term". This often comes from a history of bad experience with the community online or personal bad experience. 

Regardless of what multisexual identity a person chooses to use, it often comes down to personal preference. These are identities are not inherently harmful to one another.