Where can I learn more about Xs and Os? (NFL)

[WhoIam]

I never really got into watching football as a kid and never played played the game outside of gym class. When I went to Pitt I got sucked into the football hysteria that permeates Pittsburgh. I realized how complex the game was and started passively absorbing information on its strategy and tactics from the in-game analysts and eventually lurking on a message board where most of the posters know a LOT about football. I have an above-average understanding of the game, but I'm still not sure what people mean when they refer to certain exotic packages or what the standard strategy is certain situations. Can anyone recommend a resource, either in print or on the web where I can learn more about this stuff?