What is a data volume?

Hi,

I am trying to understand how my Symmetrix VMAX works. I have several thin pools defined from which I create LUNs that I offer to my servers. I thought that those thin pools were directly mapped into the physical storage using the specified RAID. However, I have just read that the capacity of a thin pool is taken from the data volumes. What are these data volumes? Are they thick or thin? What defines their size? Do they map finally into the physical storage? Does someone have a document that explains how does this work?

Thanks a lot