Category relates to the work type and groups a whole lot of work types grouped under category. It is a consolidation of charge codes. A whole number of charge codes will belong to a category.
Categories defines an overall grouping of different charge codes, for example if you have multiple audit charges, fixed assets, debtors, etc all these charges can be linked to categories. A charge is like a sub category and they will all add up to give you the overall totals for the category.
The above categories can further be broken down into charge codes for further analysis.