Reduction

So, do you remember that little law of thermodynamics? What was it?

Energy is never created, or destroyed, it is always transformed...

...or transferred. 

When one atom, ion, or molecule, loses a electron, this little particle cannot just run around the environment. He needs a place to stay, a house. And what kind of house am i talking about?

Another atom, ion, or molecule.

Yes, they must gain the electrons that were lost by other elements that got oxidated. 

If oxidation is the loss of electrons, than, the gain of them is called reduction.