A rotation above 1 means more shares traded than actually exist in public hands, which can only happen through repeated intraday turnover by short-term traders. It is a sign that the holder base has been entirely replaced and that the price is being set by flow rather than by valuation.
Small float plus high rotation plus hard-to-borrow status is the classic profile of a squeeze. The same reading is also a warning that the stock can retrace just as fast once the flow stops.
Example: a stock with a 6M share float trades 21M shares. The float rotated 3.5 times in one session, so the average share changed hands every couple of hours.
Related: float, days-to-cover, short-squeeze, hard-to-borrow, meme-stock