The word <obi> being used in poetry, it probably refers to a wide sash that's usually tied around the waist over a kimono. Kimono sashes for women are made of silk, brocade, wool, or cotton, quite often with elaborate embroidery, whereas sashes for men are narrower in width and less elaborate. This word is quite often used as it is(i.e. OBI) among those who are familiar with Japanese culture.