Data types contain system level and custom data types.  System-level data types are provided with the product.   Custom data types can be built and configured for use within the product.  Data types are used rendering a UI control for the step input/property.  In the new version 9.10, Data Types are displayed as a table view instead of a box view as shown below.  

For example, the decision step has a property called “condition” that is defined using the data type “string”.  When the decision step is rendered on the process designer, the “condition” step property is rendered as a text box.