A person who is engaging in heterosexual activities or has primarily heterosexual tendencies, but is also experiencing arousal by the same sex. Thoughts/visions of the same sex activity, but not yet acting on those feelings. A desire to explore intimate things with the same sex.
Typically, those who are bi-curious do eventually experience bisexuality. (Why choose? Why not have both? Be greedy...etc)
Bi-curiosity can also be a precursor to other sexual activities such as poly relationships, group sex (3-somes). (Like they say, curiosity killed the cat but satisfaction brought her back!)
Females seem to be more apt to admit bi-curiosity than males.
My girlfriend Maggie is so sexy, I just had to tell her that I'm hella bi-curious.
Girl, when another female tells you you're hot, she's gotta be at least, bi-curious!