I feel it rather important to point out so people can do the math, it is NOT a percentage. A percentage as we all know is 1 part in 100. The symbol being used is, ‰, which is per mille, or 1 part in 1000.
Cent, mille, cent mille, etc. It's the math that prob got ignored, forgotten or just plain unused by a lot of people, but those that deal with numbers and larger numbers of course, it comes into play a LOT. In any case, knowing 1 in 1000 should help you understand the numbers part instead of ignoring for just the words. Hope that helps.