What is augmented second?
An of three spelled as a second — like F up to G♯. Wider than any step a major allows, it gives the scales that contain it (harmonic minor, (פֿרייגיש)) their dramatic, 'Eastern' colour.
An augmented second is a major second widened by a half-step: three semitones between two neighbouring letter names, such as F to G♯. It sounds the same as a minor third in equal temperament, but it behaves differently — it's a *step* in a scale, not a leap between chord tones, and Western classical voice-leading treated it as an error to be smoothed away. Scales that keep it are exactly the ones that sound 'exotic' to major-scale ears: the harmonic minor (between its sixth and raised seventh) and the freygish / Phrygian dominant of klezmer (כּלי־זמר) , flamenco, and Middle Eastern music (between its flattened second and major third).