Avoid note

In jazz theory, an avoid note is a scale degree considered especially dissonant relative to the harmony implied by the root chord, and is thus better avoided. In major-key tonality the avoid note is the fourth diatonic scale step, or 11th, which is a minor ninth above the 3rd of the chord, and thus very harsh. In melody it is usually avoided, treated as a “scale approach note” or passing note, or sharpened. It is not available in harmony.