Sram:

With race-ready performance and technology, X5 components help off-road enthusiasts take it to the next level. With smooth, precise X-Glide shifting and legendary SRAM 10-speed performance, X5 brings out the best in any bike and in every rider.

ZeroLoss simply means, well, zero loss when you push on the lever, for an upshift or down shift, the cable is engaged instantly zero loss of movement. There is no middle-ground where youre waiting for the shift to come. Gear changes are instant and precise.