This article tells you something about the data main type category column definition.
When creating a new column or browsing the current definitions, the main type you assign to a certain definition, tells you what type of data is gathered here and how it is going to be used within the data garden.
Data tells you just what it is: data. The input and output of this information remains the same. When you add definitions to your database, for instance to add information that is not being supplied by the questionnaire or the system definitions such as respondent related or shop related information this is represented as static information that helps you put a perspective on your other data.
Data comes in three subtypes (or properties): text, numbers and data (calendar) format.
You can point to this type of data when creating rules or using fieldpickers and the like, but the information will remain the same.