Parts per million

The "parts-per" notations are used to denote low concentrations of chemical elements. Also known as mixing ratios, they are often used to denote the relative abundance of trace elements in the Earth's crust, trace elements in forensics or other analyses, dissolved minerals in water, or pollutants in the environment.
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one part in a million. Abbreviated ppm and commonly used to express defect levels or concentrations. Passivation - a final layer or layers put on semiconductors to protect them against contaminants and mechanical damage.

Unit commonly used to express contamination ratios, as in establishing the maximum permissible amount of a contaminant in water, land, or air.

Number of parts of a chemical found in one million parts of a particular gas, liquid, or solid. See concentration.

Parts (molecules) of a substance contained in a million parts of another substance (e.g., water).