Indie author's can come from a lot of different places.
For some people, being an indie author means you do everything on your own, from writing the book to editing, to creating the cover and formatting the book for publication. It even means building up your own marketing strategy and running advertisements for your own product.
For most people, this is too much to ask. It isn't often someone will have all of the skills needed to do this on their own, but that doesn't mean they aren't an indie author. Indie includes community, and often it means outsourcing the pieces you can't handle alone to friends or other professional who also do their job in an indie fashion.
You're still indie. You're just indie with a community. There are a lot of us out there struggling to get by without having the market powers and pressure that comes with being a traditionally published author. We do it because we love to do it, not because we're trying to get rich (it would be nice, of course, but isn't likely).
Being an indie author is primarily an approach to writing and publishing, a matter of self-definition.
If you are the creative force behind your books, from conceptualization to the finishing product and beyond, then you’re indie. If you don't allow other people to guide your book and force you into a corner (no one puts baby in the corner) then you are an indie author.
An indie author develops partnerships that deliver the best product to the most number of possible readers, trade publishers included. Sometimes that might well involve working with an agent to sell your rights, or directly with a publisher.
So, don't be afraid to call yourself an indie author, even if you've been published before. As long as you love your product and the act of making the book, then you are indie.