Basically a hybrid drive is a hard drive with a small SSD incorporated as a caching drive with clever on-board firmware that determines which sectors of the discs are accessed most frequently so as to cache them, resuting in SSD-speed loads of your most used software, and much faster computer boot times.
I've built a few computers recently using hybrid drives (also known as SSHDs) and they're a really good way to speed up a low-cost computer.