1.29 understand oxidation as the loss of electrons and reduction as the gain of electrons

In ionic bonding, atoms either lose or gain electrons (to form ions). When an atom loses electrons, it is called oxidation, when an atom gains electrons, it is called reduction.

NOTE: a useful was of remembering which is which is with the anagram 'O.I.L.R.I.G' (Oxidation.Is.Loss.Reduction.Is.Gain)