Oxidation state refers to the overall charge on an atom or molecule. It takes into account both positive charges in the nucleus and the negative charge from the electrons. It is used primarily in chemical equations when describing oxidation and reduction, or redox reactions.
It gives us the electrical state of an atom bound in a molecule, as if we hypothetically see it as ions. The oxidation state is the total charge which all the bonds of the particular atom generate considering their electronegative value. A atom which strongly attracts electrons will make his partner-atom thus more positive, giving it a delta+ charge and a +I oxidative state. Considering every bond you can make this calculation , which results in the total Oxidation State of the atom.