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.