A:Answer You can find a more thorough answer here: https://www.sdcard.org/developers/overview/speed_class/
In short, it's just how the speed of the card is classified. UHS-1 is similar to class-10 cards but is still on the faster side. UHS-1 is one step below UHS-3 which is currently the fastest. Certain devices work better with faster cards, like HD video on a GoPro, for example. Or burst shots on a high resolution digital camera.
