Comes from the Greek "ana" meaning "back" or "again" and "graphein" meaning "to write". It is a type of word play, that consists of rearranging the letters of a word or phrase in order to produce other words, using all the original letters exactly once. In a more advanced, sophisticated form of anagramming, ones goal is to 'discover' a result that has a meaning that defines or comments on the original subject in a humorous or ironic way as in Somewhere Over the Rainbow ~ Worrisome However Beneath.
Sam: Anagram, maybe?
Dean: I think it's an anagram.
Kraus: A what?
Dean: An anagram. Same letters, different words.
Dean: You know, it's, uh, maybe word fragments... other times, it's anagrams.