Its based on the Earhert-Perkins system. Charlie Weiss and BB took it a step further. Its basically concepts that allow any play to be ran out of any formation. What makes it difficult is each receiver has multiple route options on each play depending what the defense is showing. The qb and receivers have to be in sync and able to read the play pre snap, but also be able to adjust if the defense shows something different after the snap.
A lot of good receivers coulnt grasp it. Ocho Cinco comes to mind as well as Reggie wayne.
I should have stated that Allen isnt ready to run the full concepts yet. Im sure Daboll has limited the route options as well as how many and what formations he is using