What makes a mixte frame? Further, what's the etymology of 'mixte'?
A mixte is a step-through (low top tube or "ladies") frame with 3 sets of stays instead of the usual 2. The usual is that the middle set of stays run all the way to the head tube replacing the top tube, but there's some where the top tube is still a normal single tube. The traditional mixte has those axle-to-head stays straight, but I've seen designs where they're bent to give an even lower standover height. They still retain the usual chain stays and seat stays. This design keeps the frame strong and doesn't require a longer seat post.
I believe the word itself comes from french and means "mixed" as in "mix of women's and men's styles" or maybe even "unisex". Anybody around here speak french?