Although also called a sword in English, the Dao refers specifically to the single-edge blades. A Dao can be straight or curve, wide or narrow.
The broadsword is said to be the quickest weapon in China that one could be competent in. This is due to its ferocious but no-nonsense style. Hence, it quickly became the weapon of choice for the infantry in ancient China. And even as recent as the Second World War, the Dao was actively used by the Chinese soliders and resistance forces.
The practice of Dao is still very common amongst various Chinese martial arts. With fast and powerful techniques, the Dao is certainly not for the light-hearted. Hence the Chinese saying - the Dao is like a wild tiger!