[Haskell-beginners] About Data (was List of all prelude function types?)

Ive a related couple of questions: Whats with the word 'Data'? Almost every Haskell module seems to be under Data. I dont get exactly the usage of the word. Also is there some easy way of browsing up and down the hackage hierarchical structure? [I know about hoogle and hayoo. I perhaps dont know how to use them well]