O3

O3 may refer to:

==Science and technology== Ozone (O3), an allotrope of oxygen O3-|, the ozonide anion O(3), the 3-dimensional orthogonal group in group theory O3 star, a subclass of the O-type star stellar classification Haplogroup O3 (Y-DNA), a Y-DNA Haplogroup OpenAI o3, an artificial intelligence model