Klederdracht means traditional costume. Many regions had their own style. Experts can tell you what area a person in a photo came from just by looking at the style of headwear or clothing.
![family in traditional costume](https://www.dutchgenealogy.nl/wp-content/uploads/2017/06/klederdracht-e1495724643426-672x439.jpg)
Family in the traditional costume of Marken. Credits: Marker Museum, via Open Cultuurdata (CC-SA)