The term "tritone" refers to an interval (distance between two notes) which is equidistant from each end of an octave. The tritone is the middle tone of a sort of harmonic equilateral triangle.
Tritones are often used to add harmonic tension before resolution. In that situation they are referred to as "tritone substitutions".
The concept of substitution is appropriate for the Tritone Trio, because the only permanent member of the band is Dan Fellman. The other members are substituted, depending on their availablity for each gig.
So the Tritone Trio is not as much a static group as a conceptual framework for musical creativity. Like an improvised melody, each time it is played, it is a little different, new, and interesting.
Past, and potential members of the Tritone Trio include: