Short answers, pulled from the story.
A redox reaction is a chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in oxidation state, and reduction is the gain of electrons or a decrease in oxidation state. The two processes occur simultaneously and cannot occur independently.
Redox is a portmanteau of reduction and oxidation. The term was first used in a 1928 article by Leonor Michaelis and Louis B. Flexner.
An oxidizing agent removes electrons from another substance and is itself reduced, which is why it is called an electron acceptor. A reducing agent donates electrons to another substance and is itself oxidized, making it an electron donor.
The two classes of redox reactions are electron transfer and atom transfer. In electron transfer, usually one electron flows from the species being oxidized to the species being reduced, while in atom transfer an atom moves from one substrate to another, as in the rusting of iron.
Redox reactions are the foundation of electrochemical cells, electroplating such as chrome-plated parts and gold-plated jewelry, and cathodic protection against corrosion. In geology, iron oxides like magnetite and hematite and titanium dioxide as rutile are reduced to metals, often in blast furnaces where iron oxides and coke produce molten iron.
OIL RIG stands for oxidation is loss of electrons and reduction is gain of electrons. LEO the lion says GER means loss of electrons is oxidation and gain of electrons is reduction, while AnOx RedCat places oxidation at the anode and reduction at the cathode.