I went to the Ameraucana Breeders Club to get the following definitions completely unedited.
"According to the American Poultry Association (APA), the Araucana breed must be rumpless (no tail) and have ear tufts. Ear tufts are clumps of feathers growing from small tabs of skin usually found at or near the region of the ear openings. This feature is unique in the U.S. to the Araucana breed. This trait is nearly always lethal to unhatched chicks when inherited from both parents. Tufted Araucanas, therefore, are always genetically impure, i.e., they don't breed true and will always produce a percentage of "clean-faced" offspring.
The Ameraucana breed, on the other hand, has a tail and sports muffs and beard in the facial area. These characteristics are true-breeding. Other requirements of both breeds may be found in the APA's Standard of Perfection and in the American Bantam Association's (ABA) Bantam Standard.
The Ameraucana Breeders Club defines an Easter Egg Chicken or Easter Egger as any chicken that possesses the blue egg gene, but doesnt fully meet any breed description as defined in the APA and/or ABA standards. Further, even if a bird meets a standard breed description, but doesnt meet a variety description or breed true at least 50% of the time it is considered an Easter Egg chicken."
So in a nutshell:
Araucanas - rumpless, ear tuffs
Ameraucana - tail, muffs, beards
Easter Egger (EE) - any blue gene bird that doesn't meet APA or ABA std or doesn't breed true at least 1/2 the time
Hope this helps clear up the confusion.