What is the oxidation state of the atoms of a given element? Why is the oxidation state called the conditional charge

What is the oxidation state of the atoms of a given element? Why is the oxidation state called the conditional charge of an atom in a molecule? What condition is assumed for this?

The oxidation state is the conditional charge of an atom in a compound, calculated based on the condition that all bonds in a compound are ionic.
The oxidation state is a conditional charge, because in all compounds except lithium with fluorine, only a partial displacement of electrons from an atom with a lower electronegativity to an atom with a higher electronegativity is observed. But when placing the charges, we still assume a complete mixing of electrons for convenience.

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