Noun, Contraction of "Transsexual" or "Transgender" and "Lesbian". A Male-to-Female Transsexual who is exclusively sexually/romantically attracted to other Male-to-Female transsexuals.
The participants in a Transbian relationship can be at any stage in their Transition, from just starting out, to postop. There are quite a few Transbians in the Transsexual community, and Transbian sex is the most awesome sex out there.
Transbianism is a phenomenon few can explain, but many feel that the sexual/romantic attraction between two Male-to-Female transsexuals arises primarily from the fact that the two participants in the relationship have a shared life experience that is not common to most people, and are thus "Kindred Spirits" of the truest, most profound kind.
(Convo between two M2Fs in a Transbian relationship): Oh, baby..... I wanna make sweet Transbian love to you <3.