At times, I've heard native Russian speakers say что что, instead of single что. For example,
(I say something that is incomprehensible to a waitress.)
Is there any difference between что-что and just что? I feel like this is usually used by young women, while men and older women don't say it that much. I also feel like there are other such words (relatively short words) that are often reduplicated, but I'm not sure. Are there perhaps indeed such words, and why are they reduplicated?