Noun

1. The proportion of a substance in a mixture.
   1. The amount of solute in a solution measured in parts per million (ppm)
2. The act, process or ability of concentrating; the process of becoming concentrated, or the state of being concentrated.
   1. The act, process or product of reducing the volume of a liquid, as by evaporation.
   2. The act or process of removing the dress of ore and of reducing the valuable part to smaller compass, as by currents of air or water.
3. A field or course of study on which one focuses, especially as a student in a college or university.