As I understand it, the Araucana is a rumpless (no tail bone) bird from South America that lays blue eggs (usually, and due to an overexpression of a biliverdin transport molecule in the oviduct). Unfortunately, the rumpless gene is linked to some other kind of genetic problem. So, someone decided to cross Araucana with some other breeds, to try to breed out the rumplessness and the related defect. The result of that effort is the recognized Ameraucana breed.
"Easter Eggers" are not a recognized breed - that's an informal term with somewhat variable meanings to different people. I think of it like a general category name. Sort of like how GMC makes lots of different models of "truck", but "Truck" is not the actual model name for any of them. EE's (and OE's - "Olive Eggers") are usually crosses of different breeds (blue, light brown, dark brown, and/or white layers, trying to create as many different egg colors as possible. Some people include recognized breeds like Ameraucana and Legbar in the "EE" category - it's fine to do so, since there is no standard definition of "Easter Egged". But it's dishonest to call an EE "Ameraucana" if you bred it from other breeds.
