GT/s stands for "Giga transfers per second". It's an engineering term to avoid confusing IO transfer rates across a bus from the reference clock rate used to trigger those transfers. For example, DDR3-1600 is often marketed as "1600Mhz" but the "Double Data Rate" means that there are two IO transfers across the bus for every IO bus cycle. These transfers happen on both the rising edge of the clock, and the falling edge of the clock. Thus, DDR3-1600 should be more accurately marketed as "800Mhz; 1600MT/s" because the IO bus reference clock is 800Mhz, but the transfer rate is 1600MT/s