Musical sevenths are intervals of seven notes in a scale, usually consisting of a major seventh and a minor seventh. They are used in many genres of music, including jazz, blues, and classical music. The term 'TIS' is an abbreviation for the musical interval of a tritone, which is also known as an augmented fourth or diminished fifth. It is an interval of three whole steps, or six semitones, and is considered to be dissonant and unstable.