4O

4O is a designation used in several fields to denote a combination of the number four and the letter O. There is no single, universally accepted definition; its meaning depends on context.

Science and technology contexts often interpret 4O in relation to oxygen-related notation. In chemistry, O4 denotes a molecule consisting of four oxygen atoms and is used in discussions of oxygen clusters and high-oxidation-state chemistry. A related species, tetraoxygen (O4), has been observed as a transient in gas-phase and solid-state studies. The notation '4O' may appear informally in reaction schemes to indicate four oxygen atoms participating in a process, but this is not a standardized chemical symbol.

In technology and branding, 4O has been adopted as a model or series name by various companies. The designation is typically company-specific and conveys branding rather than a universal property.

In culture and typography, the combination '4O' is also used in codes, artistic titles, or fictional works, chosen for its visual symmetry and mnemonic appeal. Because the characters '4' and 'O' can be confused with '40' or '0,' the string is sensitive to font and rendering.

See also: O4, O2, tetraoxygen, stoichiometry.