A neutralization reaction occurs when an acid is mixed with a base. The products are salt and water.
Neutralization continues until all of the ions of either the acid or base are used up. In a fully neutral solution, the concentrations of acid ions and base ions balance out, and the pH of the solution is 7.
If you mix equal amounts and concentrations of HCl (hydrochloric acid) and NaOH (sodium hydroxide), the Cl- and Na+ ions will combine to form NaCl, and the H+ ions and OH- ions will combine to produce water. The resulting mixture at equilibrium will be a neutral salt solution.
If you mix a higher concentration or greater volume of HCl to NaOH, then there will still be an excess of H+ ions in the mixture at equilibrium. As a result, the mixture will be acidic, rather than neutral.
The reaction of a strong acid and a strong base is very violent because a lot of energy is released in the process. This is the reason why strong acids should always be neutralized using a weak base and vice versa.