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Explanation: I'm sorry I don't have an answer either, but the ones you suggested, as far as I know, design a certain type of sail - one which can be rolled. And the Duden says a "Reff" is the device for rolling the sail. I went for a sailing trip a few years ago, but I don't remember there being a word for the part of the sail that is rolled - which isn't saying much. In the link below, you will find "die gereffte Segelfläche" (ausreffen), which doesn't sound very nice but maybe that's all there is?