Nhat Binh literally means square-collared garb. This was one of the casual clothes of the empress dowager, empress consort, and princesses in the imperial city of the Nguyen Dynasty – the last dynasty of Vietnam. When there were informal events, these royal women would wear the ao Nhat Binh instead of the Phuong bao (means the garb of phoenix), which was the noblest clothes of the empresses and princesses. For consorts, female officials and those ladies with high social status, ao Nhat Binh was their noblest clothes.
Ao Nhat Binh is a straight-collared garb, whose collar dangles down, making two parallel lines. The origin of ao Nhat Binh was from Phi Phong garb, which was popular in the Ming Dynasty of China. When wearing ao Nhat Binh, wearers tie a knot with the pieces hanging from the collar in front of the chest and decorate (to hide the knot) with a sculpted gem. On the collar are flowers and phoenix patterns. The garb may be plain with one color or can be embroidered with many circular patterns. On the cuffs, there are five colored lines which are green, yellow, blue, white, and red representing the Five Elements wood, earth, water, metal, and fire.