What is subtonics?

Subtonics are musical chords or notes that are one half-step below the tonic note or chord in a key. They are also known as "lower leading-tone chords," as they are often used as a transition or passing chord to lead to the dominant chord in a key. Subtonics are indicated by the Roman numeral VII in a major key and vii in a minor key. They can add tension and interest to a musical passage, and are commonly used in jazz, blues, and classical music.