MEMS are micro electromechanical systems. As I understand it, that pretty much means they’re tiny chips with moving parts.
The example the team at GE gave us to help us understand how and why they matter is circuit breakers. Think of the box you have at home that’s full of a bunch of black switches which trip if there’s some sort of surge. Those things take milliseconds to flip open and protect, during which time the current can rise to thousands of amps, which could short something. With a MEMS breaker, however, that time is limited to microseconds, thanks in large part to the fact that the switch just has less distance to travel (it’s the difference between turning a light switch the size of the one on your wall and one that would fit on a microchip).
Here’s the MEMS team explaining:
(If you are looking to learn more about circuit breakers, head on over to How Stuff Works, though I think I’ve done a fair job describing it.)
Where this technology becomes especially interesting is in large industrial settings where you might be dealing with millions of dollars of equipment. Frying something at that size can have a big impact on business. Craziness.