The term 'O' on the periodic table refers to OXYGEN, which is a chemical element with the symbol O and atomic number 8. OXYGEN is the third most abundant element in the universe and makes up about 20.8% of the Earth's atmosphere. It is a colorless, odorless, tasteless gas that is essential for all known forms of life. OXYGEN is also the most important component of air, and it is necessary for respiration in animals and plants.