The one-and-a-half ratio: three units spread across two matras, so strokes coincide with the beat only every other beat, the rest landing squarely between. Aad is the first of the "crooked" layas and the signature of the Ajrada school's kaida development.
It is practiced by anchoring the tala with claps or lehra while the hands hold the 3:2 grid without drifting into triplets-per-beat (that would be tigun). Once aad is stable, kuad (5 over 4) and biad (7 over 4) extend the same principle. The mark of command is conversational ease — phrasing freely in the ratio while the cycle stays untouched.