This article tells you something about the questionnaire 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.
Questionnarie data is all data that is being gathered by filling out your questionnaire. These columns are created when you add pages to your questionnaire and answer options to your question pages.
The actual answers a respondent provides by filling out the questionnaire are translated into a code which is shown when browsing the data view of your data garden.
For instance: let's say we have a single response question: "How often do you use our service?", to which a respondent can answer by clicking "Daily", "Weekly", "monthly", "Yearly" or "Other".
The datagarden doesn't show you the exact answer but a code that it is translated into:
"Daily" = 1
"Weekly" = 2
"Monthly" = 3
"Yearly" = 4
"Other" = 5