The word "rewind" is often used in reference to audio or video recordings. It means to go back to a previous point or to play a recording backward. The phrase "Whoa! ... say what?!" could be indicating surprise or confusion, perhaps suggesting that the concept of rewinding is unexpected or unfamiliar to the speaker.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: "Whoa! ... say what?!". Explanations are generated by AI and may be inaccurate.