What is unresolved leading tone?

An unresolved leading tone is a note that is a half step below the tonic in a scale, which typically creates a sense of tension or anticipation. In tonal music, the leading tone usually resolves up to the tonic, but when it remains unresolved, it can create a feeling of instability or openness in the music. This technique is often used to prolong harmonic tension or to create an ambiguous or unresolved atmosphere. It can be found in various genres and styles, contributing to the emotional effect of a piece.