From The Last Resort:
"A cheese curd is an orangish cheese byproduct that feels like Silly Putty but tastes a lot better. It was invented accidentally by UW cheese scientists attempting to create an object of pure cholesterol that would still squeak. Rats who are fed this remarkable food develop an unusual capacity to polka and drink beer."
But seriously, folks, cheese curds are fresh, young cheddar cheese in the natural, random shape and form before being processed into blocks and aged. (Cheddar cheese is typically aged from 60 days to 4 years before being sold.) Unlike the aged variety, curds lose their desirable qualities if refrigerated or not eaten for a few days (the squeak disappears and they turn dry and salty).
Yes, cheese curds really do squeak! There's also a recipe for Deep-Fried Cheese Curds that just sounds yummy.