I don' understand what are the 'Registered data'

Hi, in both the folders Abdomen and Cervix we have the RawData, Reg-Training-Training, and Reg-Testing. What are Reg-Training-Training and Reg-Testing? I saw the description and I really don't understand what "registered data" means. What is the difference compared to RawData? Can I use Reg-Training-Training and Reg-Testing to train my model? Are they the famous extended version of the dataset that I read about on the internet? If this is not the case, where I can find the extended version of the dataset with 80CT scans? Thanks for the answer