It means that the economy is dividing into high-skill, high-wage jobs and low-skill, low-wage jobs -- and that the middle, the middle-skill jobs, and the middle-earning jobs, are starting to drop out of the economy.
这表明经济被分为高技术、高薪工作 和低技术、低薪工作-- 在这中间，中等技术工作， 中薪工作正愈消亡。