What's the difference between an item category and a browsing category?

Item categories are also known as purchasing categories and are used to group items for various reports and programs. Every item must belong to an item category.

Browsing Categories, also known as navigation categories, define the category hierarchy for category browsing or for category grouping. They can be either parent or child to another category, but they cannot contain any items. They are used as navigation categories to help users browse for items.