I think that the meaning of "indie developer" has changed throughout time. Back when I first started programming the people around me considered indie teams to be a development team that was not associated with a publisher. The "indie" part came from being independent of any 3rd party. This was before everything went digital however... Now anyone can publish a game without a large amount of capital and they're not forced to depend on publishers.
I've also found that many people define "indie" differently to being smaller teams, lower budget teams, teams without publisher influence, ect...