Neutralisation is a reaction between acid and base to form salt. Most salts are neither acidic or basic (doesn't contain neither H+ nor OH-). They are neutral (pH = 7). That's why such reactions are called neutralisation reactions. For example, the most common neutralisation reaction is HCl(aq) + NaOH(aq) = NaCl(aq) + H2O
HCl + NaOH = NaCl + H2O Acid pH<7 Base pH>7 Salt pH = 7 pH = 7 As it is shown above when we mix equal amounts of acid and base we have pH = 7 in the result which is neutral. In that way acid neutralise base or base neutralise acid.