Trannyboy is a term denoting a female-to-male (FtM) transsexual person. FtM individuals may or may not choose to transition their bodies to their proper gender using hormone therapy or SRS.
As with many terms for transgender individuals, the term "trannyboy" should be used with discretion. Some members of the trans community might find a given term offensive where others do not.
Steven was born female-bodied but identifies as a male. He lives and presents himself as male, and calls himself a "trannyboy".