A contraction of the phrase "transsexual lesbian". A transbian is a male-to-female transsexual who is also a lesbian - ie. a transsexual woman who is sexually attracted to other women.
"Probably more than half the trans women I know are transbians or bi. Fewer than half are straight."
Straight/bi men with a lesbian fetish so intense that they started calling themselves lesbians. Frequently complains about cis lesbians not wanting their “organic strap”, aka male genitalia.
transbian: this cis lesbian at a lesbian bar turned me down!