Redox refers to a substance gaining an electron and releasing what?
Redox chemistry relates to electron transfer: the formal loss or gain of electrons.
A substance that accepts electrons is an oxidant, an oxidizing agent:
In accepting the electrons it has in fact been reduced.
A substance that donates electrons is an reductant, a reducing agent, and in losing those electrons it is itself manifestly oxidized:
We include electrons in these half equations, as a means to help balance with respect to charge. We add the half equation together to remove the electrons from the final redox equation:
In all instances, charge must be balanced as well as mass.