A yếm is a traditional Vietnamese undergarment worn by women. It's like a vest that covers the chest and stomach area. It's made out of soft fabric like cotton and has ties on the sides to keep it secure. The yếm is usually worn underneath a long silk tunic called an áo dài. It helps to keep the chest area covered and supported. Think of it like a superhero's suit under their clothes that helps them look and feel strong. The yếm has been a part of Vietnamese culture for a very long time and is still worn today by many women for special occasions or cultural events.