Oxidation and Reduction are two sides of the same coin. When something is oxidized, something else has to be reduced, and visa versa.  The process of oxidation-reduction involves the transfer of electrons. Oxidation is the taking or receiving of an electron, while Reduction is the giving or the losing of an electron. Oxidation-reduction is a process or verb, while the state of being oxidized or reduced is an adjective.

How aggressively an oxidizing agent takes an electron will affect its tolerance to living tissues. Some powerful oxidation-reduction reactions occur within the mitochondria, the small furnaces that provide energy to each cell.

Summary

Oxidation is the taking or receiving of an electron, becoming more negative. Oxidizing agents cause oxidation of their target, which means that they take an electron from the target. However, the target is reduced during oxidation!

Examples of powerful oxidizing agents are acids, which have an excess of of H+ ions, which are seeking electrons, negative particles that combine with the positive H+ ions.

Reduction is the giving or losing an electron, becoming more positive. Reducing agents cause reduction of their target, which means that they give  or force an electron upon the target. However, the target is oxidized during reduction!

Bases can be powerful reducing agents, in that they force their electrons upon their target.  Examples are lye, chlorox.

Most acids are oxidizing agents.

Most bases are reducing agents (donate electrons)

Most Anti-Oxidants are reducing agents (including vitamin C, glutathione, iodide)

References

Oxidizing and Reducing Agents

Oxidation-Reduction Reactions