A liquid lens is pretty much exactly what it sounds like. The really cool thing about them is that, though they have no moving parts (unless you count the liquid itself), they can achieve a pretty wide range of dynamically-variable focal lengths over a relatively short optical path. When I first read about them, the killer app was supposedly going to be phone cameras.
Anyway, in this, his most recent vid, übermaker Ben Kransnow explains not only what a liquid lens is and how it works, but how he managed to get his hands on one to play with by ripping it out of this “snake” autofocus webcam. I note that the manufacturer is now selling this camera, in the US, on eBay, though their feedback rating is not great. Once you have the lens module in hand, apparently getting a driver IC to talk to it is another ball of wax. Ben explains nicely, as usual.