UHS stands for “Ultra High Speed” and refers to the new technology that enables higher bus interface speeds on Secure Digital High Capacity (SDHC) and Secure Digital Extended Capacity (SDXC) cards.
UHS-I defines interface speeds up to 104MB/sec. A SDHC or SDXC card that supports “UHS” could have performance up to 104MB/sec.
UHS-II is the next generation of UHS. UHS-II improves the interface speed up to 312MB/s. That is 3 times faster than UHS-I.
*Source: SD Association