In the Mac world, and now iOS which most of this article refers to, the term indie developers has a more specific meaning. It refers to a single developer or small team of a few developers that is self-funded. It almost definitely implies doing it full-time [1], and not doing this during their free time only (aka. hobbyist).
It has more or less the same meaning as used in the video games community, and similar to how it's used in film making.