An idividual who is assigned a feminine gender role at birth to concure with hir female sex; in actuality ze has a masculine gender identity and lives as a boy all or part of the time. Tranny boys are in the early phase of transitioning from female to male and have either just begun or have not yet begun medical intervention(such as hormone therapy).

a tranny boy is a boy who is really a girl. A tranny boy can fool somebody into thinking they male at first but then they find out they female. Trannny supriseeee!