(a) A jabberjay is a genetic mutation from the series The Hunger Games by Suzanne Collins, used for the war during The Dark Days (the rebellion of the people against the government). After the war, they bred with mockingbirds to produce mockingjays.
(b) A "Jabberjay" is also what die-hard and totally obsessed fans of aforementioned series call themselves.
The jabberjays could memorize long passages of the District people's plans - but eventually, the District people started feeding the Jabberjays lies, making them utterly useless.
I got Mockingjay the first day it came out and red it in thirty minutes flat. I am such a total jabberjay.