To make the site structure more logical and coherent, each page in the site is assigned to a category. For example pages talking about policies are in Policies –category, pages talking about instruments are in Instruments –category and pages talking about individual products are in Products –category.
The categorization is hierarchical. All pages in Policies belong to category Policies and instruments and so on.
This is the most toplevel category. This category divides into smaller categories for different types of pages.
Here is a list of all the categories and subcategories in the wiki (click here for a graph):