A netcast is an MP3 file or other rich media file that is listened to or watched on the internet via a direct link to the website. But does not have an RSS feed from which to subscribe to. It is essentially a webcast. It is not a Podcast where one can subscribe to a show via iTunes or other aggreagator.
Person A: "Hey did you subscribe to that new Podcast about Basket Weaving."
Person B: "No it is just a Netcast and will not let you subscribe via RSS"
Person A: "Bummer"