A RiddleMeThis Questionnaire is saved in a folder (or directory if you prefer) containing a file describing the Questionnaire's structure (this file is always called form.rmt) and possibly some sub-folders.
Test Data contains session data from testing your questionnaire. You can safely delete this folder if you want to reset your test data or simply to save space (e.g. when emailing your RiddleMeThis projects to colleagues).
Data contains session data from running your questionnaire. If you've made major changes to a questionnaire, you may want to delete or archive the contents of this directory, or simply rename the folder, to avoid corrupting new data with old data from an obsolete version of your form.
Images contains any images required by your form (and possibly old images no longer used by your form). These images are stored as high quality JPEG images.
Videos contains any videos required by your form (and possibly old videos no longer used by your form).