I just tried subscribing to a podcast (I won't shame the particular podcast, outside of saying that they should "know better", but I have two things that (to me) mean you can call your serial show a podcast:
- It has a RSS feed plainly available as an RSS feed (and not just an iTunes feed)
- The audio is not buried somewhere on Soundcloud or some other locker-type service where it can't be put onto a portable device.
I can't tell you how many shows I've seen that violate these principles. You don't have a podcast; you just have a radio archive at that point.