Himyaan is the waistband of lower garment of Ihram. It is a belt or a strap a pilgrim fastens around his waist and a pocket to keep money in.
Ataa’, May Allaah Have mercy upon him, said that a pilgrim is allowed to wear rings and waistbands. Ibn ‘Umar, May Allaah Be Pleased with him, made Tawaaf in the state of Ihraam, while he was fastening a piece of cloth around his waist.” Most scholars held that a person in the state of Ihraam is permitted to wear a Himyaan. Chapter of Saheeh Al-Bukhari 1537