Tap dance's basic building block: a brush forward plus a brush back in one motion — two audibly separate tones, with no weight on that foot. Brush plus step with full weight would be a flap.
Almost every combination in tap stands on a handful of building blocks — and the shuffle is the one running through all of them. A clean shuffle carries every choreography you learn later; a sloppy one drags through your entire repertoire. The typical error is one tone instead of two, which happens when you stamp rather than letting the foot drop loosely, or when the tempo outruns the technique. The fix is unglamorous: slow right down and count “one-and” out loud until forward and back sound clearly separate and both tones are equally loud. What gets missed: your floor lies to you. Laminate over underlay springs everything away, carpet is out entirely. A shuffle that sounds clean at home can be mush on studio parquet — so calibrate on a real floor at least once a week.