What is "t-tail"

n. (''aeronautical'') Type of aircraft that has the horizontal stabilizer situated atop, or near the top of, the vertical stabilizer.

A T-tail is an empennage configuration in which the tailplane is mounted to the top of the fin. The arrangement looks like the capital letter T, hence the name. The T-tail differs from the standard configuration in which the tailplane is mounted to the fuselage at the base of the fin.