Ozone is a molecule composed of three oxygen atoms. While oxygen normally combines in pairs of two, bombardment by ultraviolet light in the upper atmosphere causes them to form groups of three. Ozone is also formed during corona discharge.
Properties of Ozone:
Ozone has a sweet, saccharine-like smell/taste. It's rather toxic, even in small amounts inducing nausea and vomiting. Whee. Ozone is also used to sterilize water, and sometimes air.
A final word of caution: Ozone is corrosive, just like normal oxygen. Handle With Care!