Three semitones. Defines the minor character — soft, dark sound.
Root on string 4, fret 0. Interval on string 4, fret 3.
The minor 3rd is one of the most widely used intervals in music. It underpins all minor chords and scales. The blues scale without a minor 3rd is unthinkable. The "Smoke on the Water" riff begins with a minor 3rd. In classical music, minor keys (and the minor 3rd) are associated with drama and depth.
Memorize the opening of "Smoke on the Water" — it is an ascending minor 3rd. Practice singing the interval from any note. On guitar, a minor 3rd is three frets on one string. Compare minor and major 3rds by ear — this is a key skill.
Learn to recognize intervals by ear with the interactive trainer.