CH3COOH is considered a weak acid because when diluted it does not get completely dissociated to liberate the H+ ions i.e. CH3COOH upon dilution liberates a very small amount of H+ ions and considered a weak acid. HCl on the other hand upon dilution dissociates completely to generate the H+ ions and liberates a huge amount of H+ ions per unit volume and hence, considered a strong acid.
