Hakama

Found at japanesekimono.com

Hakama
Hakama is an outer garment worn over the kimono that are either split
between the legs like pants or non-split like a skirt. Hakama pants
originated as an outer garment to protect samurai warriors legs from
brush when riding a horse. Today, the hakama is worn as formal attire
for ceremonies, traditional japanese dance, artists and martial arts.