A traditional Japanese tube/straight-sleeved jacket worn during festivals. Has a thick border (usually black in color) running down the coat opening, with the jacket length usually reaching between the hips and waist. The happi may be worn open or fastened closed with the use of a cloth belt. The sleeves are usually on the shorter side, but can also reach the wrists.
Traditionally indigo or brown in color, though other colors exist.
For a type of traditional indoor winter jacket, use hanten (clothes).
A similar Japanese garment called haori has wider kimono-sleeves, and is typically of a heavier fabric.
This tag implicates japanese_clothes (learn more).