Buffer

Yes.

When u adding SMALL AMOUNT of different concentration of HCl and NaOH,
only small change in pH value.

half-neutralized ethanoic acid: CH3COO-(aq) & CH3COOH(aq)

Addition of NaOH:
CH3COOH(aq) + OH-(aq) ----> CH3COO-(aq) + H2O(l)

Although NaOH is a strong alkali, OH-(aq) reacts with CH3COOH(aq)
to form neutral ion CH3COO-(aq)

Addition of HCl:
CH3COO-(aq) + H+(aq) ----> CH3COOH(aq)

Although HCl is a strong acid, H+(aq) reacts with CH3COO-(aq)
to form weak acid CH3COOH(aq)