iTunes Custom RSS Tags - Block
The iTunes Block tag is specifically designed to tell iTunes to ignore a particular post in your podcast feed. This might be particularly useful if your feed combines text only posts and posts containing audio enclosures, because the text only posts are useless in the context of iTunes RSS support. Another potential use for this tag is to exclude an episode that is intended for a select audience (say subscribers using iPodderX, for instance). The Block tag is entirely optional and should only be used in those cases where you don't want a post to show up in the iTunes Music Store.
To implement the Block tag in your RSS 2.0 feed, include the following in the <item> for your post: