Parts per million (ppm) is a common term used in science, industry, and health regulations to express the concentration of a particular substance in a solution. However, there are alternative terms that can be used interchangeably with ppm, such as milligrams per liter (mg/L), micrograms per liter (µg/L) or nanograms per liter (ng/L). These units are widely used in research studies, water quality testing, and environmental monitoring to measure the presence of pollutants or contaminants. Other synonyms for ppm may include parts per billion (ppb), parts per trillion (ppt), and percent (%), depending on the context and level of precision needed. Ultimately, all these units are used to express the same idea, which is the amount of a particular substance present in a given volume of liquid.