Waste yarn is usually just a scrap of yarn used to thread through some stitches to put them on hold for a while.
Rows with wraps are a way of shaping a piece, by inserting extra rows in the middle of a row. They can be used to shape the heel of a sock, for adding more room in the bust of a sweater, for adding curve to an elbow, or adding height to the back neck of a sweater, to name a few!
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