1, The full form of O is Oxygen. It’s used on Academic & Science ,Chemistry in Worldwide

Oxygen (symbol: O) is a chemical element with atomic number 8. The name oxygen is a combination of two words “oxy”, meaning acid and “gen”, meaning to generate or produce, hence the french word “oxygène” (acid producer). The most common characteristic of oxygen is its ability to combine with other substances to form acids.

2, The full form of O is Oh. It’s used on Academic & Science ,Language & Linguistics in Worldwide

Oh (O) is used as a response or a comment on something that has just been said. Also used to express strong emotion, such as surprise, fear, anger, or pain.

3, The full form of O is Oberst. It’s used on Governmental ,Military in Germany

Oberst (O) is the highest staff officer rank in the German Army (Heer), German Air Force (Luftwaffe).

4, The full form of O is Pyrrolysine. It’s used on Medical ,Biochemistry in Worldwide

Pyrrolysine (Pyl or O) is an alpha amino acid.