The diagram represents an oxygen ion with a -2 charge.
The Lewis dot structure of a chemical specie represents the electrons present on the outermost or valence shells of atoms in the specie as dots. Lewis structures are used for ions, free atoms and molecules.
Oxygen is a member of group 16 hence it has six electrons in its valence shell. The specie shown in the image has eight valence electrons implying that the oxygen atom gained two valence electrons when the specie was formed.
When oxygen gains two electrons it is said to have acquired a charge of -2. Hence, the diagram represents an oxygen ion with a -2 charge.
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