What is ppm meaning?

PPM stands for "parts per million" and is a commonly used unit in chemistry and industry to measure the concentration of a particular substance in a mixture. It represents the number of parts of a substance per million parts of the mixture. For example, if a gas contains 10 parts of a certain chemical per million parts of gas (or ppm), then the concentration of that chemical is 10 ppm. PPM can be used to measure the concentration of many substances, including pollutants in air and water, chemicals in food and pharmaceuticals, and gases in industrial processes.