This list contains all work types you perform for your clients. It could be translation, proofreading, DTP, etc.
Work type is used when you add a new detail row to the project. When setting default rates, you can select different work types as the basis for the rate. For example, translation usually counted on per-word basis, while proofreading tasks are counted on per-hour basis.
In addition to setting default rates, work types are used to calculate different stats of your performance.