Omnisexuality is most often defined as the sexual attraction to people of all gender identities, wherein gender plays a role in one's attraction, and it can more broadly be described simply as the sexual attraction to all genders. Some omnisexual people may be more attracted to certain genders, but that is not always the case.
The term "omnisexual" is derived from the Latin prefix omni-, meaning "all" or "universally".
The omnisexual pride flag was designed in 2015 by Tumblr user pastelmemer. It is a pink, dark purple/black, and blue flag, designed to represent the attraction to all genders. The colors represent the wide spectrum of sexual attraction, with the pink and blue shades symbolizing attraction to femininity and masculinity, respectively. The dark purple (sometimes black) stripe in the middle represents the attraction to all other genders that are outside of the gender binary.
Though very similar in the sense that both sexualities are attracted to all genders, the main difference is that pansexual people are often referred to as "gender-blind", meaning they may be attracted to people regardless of gender, whereas omnisexual people typically do recognize the gender of those they are interested in, therefore letting it play a part in their attraction.
Bisexuality, due to the prefix bi-, is the sexual attraction to two or more genders, whereas omnisexuality, composed with the prefix omni-, is the sexual attraction to people of all genders. There are nuanced differences, however, and someone who is attracted to all genders may still identify as bisexual.
Omnisexuality and polysexuality are similar in that they both describe sexual attraction to multiple genders, often with gender playing a factor in that attraction. Polysexual people, however, do not necessarily experience attraction to all genders, while omnisexual people do.
Perceptions and discrimination
Because omnisexuality is still a lesser-known sexuality, many omnisexuals may be seen as 'crazy' or mocked for having a 'fake sexuality', when in reality, there are so many more sexualities out there than the common ones already established. Omnisexual people may find their sexuality gets confused with other orientations such as pansexuality and bisexuality, and thus feel pressure to conform to a more widely recognized label just to make it easier for others to understand. They may even get forced into more common labels by others without much regard for the clear distinctions. If you come across someone with a lesser-known sexuality, the best thing to do is try to understand, listen instead of dismissing them, and most importantly, accept them for who they are.