Omnisexual often can be interchanged with the term Pansexual, though there are those who will argue the two are different. Omnisexuals are people who feel attraction towards people of any gender and orientation, including male, female, genderqueer, transvestites, bisexuals, straight, gay, lesbian, asexual, and so on. Omnisexuals see people for their personalities rather than their genitals or gender identity. Omnisexual is not a cover term used for people who will date transsexuals. Bisexual, Gay, Straight, and Lesbian SHOULD cover these terms. A well known phrase of the Omnisexual/Pansexual community is "Hearts Not Parts".
A famous example of an Omnisexual is Captain Jack Harkness from Doctor Who or Torchwood. If it has a pulse, he'll flirt with it. If it doesn't... He'll probably do it anyways.
The word Dyke was originally a slur, but nowadays it is used as a derogatory term to refer to women who are attracted to women, also known as Lesbians or Sapphists. Though a few women who identify under this sexual preference find this term alright, most of them will find this term highly offensive. The word Dyke is more often then not used in cruel way.
The word Dyke does NOT refer to transsexual men. They are MEN, not WOMEN.
Rude: "Did you hear that she kissed some girl? Ew, what a freaking dyke!"
Neutral: "She likes girls, so I guess that makes her a dyke, right? Okay, cool."
Note: The term dyke is hardly used in a "good" or "nice" way.
Bisexual is a term used to describe someone who is attracted to exactly 2 genders; male and female. "Bi" means "Two". This SHOULD include Transsexuals, for they too are either male or female. The term Bisexual does not encompass sexual or romantic attraction towards genderqueers, genderfluid people, transvestites, or other genders aside from male and female. If one finds attraction towards people outside the gender identities of "male" and "female", it is quite possible they fall under a different sexual preference label.
John is attracted to Jane, who is a transgendered woman, and Jo, who is a cisgender man. He is Bisexual.
Jane is attracted to John, who is a transgendered man, and Jill, who is a cisgendered woman. She is Bisexual.