since you're posting this in graphics cards, im assuming you mean ASIC quality.
every card has an asic quality. an "asic", or "Application Specific Integrated Circuit", is effectively a circuit designed to perfectly do a given job. our gpus are designed to compute. however, due to the nature of the manufacturing process, no die is perfect. your percentage, or quality, is how close you are to a perfect chip.
people brag about their asic quality because it loosely correlates to overclocking potential. usually lower percentages mean higher voltage leak, and less efficiency, so a higher asic usually means you can push the card farther with an overclock before it becomes unstable.
some manufacturers even bin their dies(sort them) for better asic and put the better ones in gpus they can market as having 80+ or 85+ asic. usually for an extreme price premium. dont really see it being worth it myself unless you're trying to win a world record for overclocking.
as for everyday use, it means nothing really, especially if you're not going to be overclocking. if you are, it may limit your overclocks if its low, it may not.