I have seen Casper FFG described as a "finality gadget". For example here:
Casper FFG is a “finality gadget”, meaning that it describes the rules for finality of blocks, and detects the finalization of blocks after the fact.
The way it is states makes it look as if "finality gadget" is a separate, distinct concept. But I can't seem to find any independent definition of the word.
Does anyone know if it is indeed a distinct concept, or something that was invented as part of eth2?