This is one of those questions that you will never get a clear answer. People have diffrent deffinitions.
I go by an Independent game is a game released without a publisher. An Independent Developer is a Developer not owned or associated with a Publisher.
IE. Epic Games is an Indie dveloper because they are not a subsidiary of any publisher (although it can be argued they are one themselves) although most of their games are NOT Indie games since they are published by Microsoft. Naughty Dog on the other hand is NOT an Indie developer because they are a subsidiary of SOE.
Then of course you have all your games and developers that are "obviously" indie that most people associate "Indie" with. IE. Almost every game featured on this site
I prefer not using the term indie at all just because of how much baggage comes with the term.
Indie is normally associated with limited resources (Money, Manpower, Exposure).
My Definition is any game or developer without an external publisher (Which includes an ENORMOUS, population everwhere from Flash to AAA games).