The abbreviation "H2O" represents water, which is a chemical compound composed of two hydrogen atoms bonded to one oxygen atom. It is essential for all forms of life, acting as a solvent in biological processes, regulating temperature, and facilitating nutrient transport within organisms. Water is unique in its properties, such as high surface tension and the ability to exist in solid, liquid, and gas states. Its significance spans across environmental, biological, and physical sciences, making it a vital resource for health and ecosystems.