The Haori (羽織) is a vital component of the traditional Japanese fashion. It is a hip- or thigh-length kimono-style jacket, typically worn during festivals or ceremonies.
The haori does not close like the yukata, but is worn open or kept closed by a string that connects the lapels.
It is meant to simply be put over what you are wearing and in many resorts and hotels in Japan you will be given a haori to wear in your room like a morning robe.
In the past haori were worn by men in battle as overcoats to protect against the cold, but in the modern era they are typically worn as jackets over kimono by women.
The Haori was not worn by women until the Edo period (1615-1868) when geisha started to wear the garment in imitation of men's kimono attire.