What is considered explicit?

I'm not sure that there is a clear cut definition. It's relative to what an individual would consider explicit.
For the most part I think that iTunes podcasts are "listener" regulated. Meaning that if you have a podcast that someone deems inappropriate or explicit, they can report it by clicking the "report a concern" button on the podcasts' iTunes directory page. Then the iTunes staff makes a decision.
The iTunes podcast tech spec:
http://www.apple.com/itunes/store/podcaststechspecs.html
has this to say about the Explicit tag:
<itunes:explicit>

This tag should be used to indicate whether or not your podcast contains explicit material. The three values for this tag are "yes", "no", and "clean".

If you populate this tag with "yes", an "explicit" parental advisory graphic will appear next to your podcast artwork on the iTunes Music Store, and in the Name column in iTunes. If the value is "clean", the parental advisory type is considered Clean, meaning that no explicit language or adult content is included anywhere in the episodes, and a "clean" graphic will appear. If the explicit tag is present and has any other value (e.g. "no") you see no indicator — blank is the default advisory type.

Which says that "Clean" would indicate that there is absolutely no explicit content and "yes" contains explicit content. Which confusingly leaves "no" in a kind of limbo.

When in doubt, add the explicit tag...perhaps one swear (say the s-word) word wouldn't perhaps deem the whole thing explicit, but a whole litany of them might. You can add it for the entire feed by putting the tag at the <channel> level or on a per episode basis by putting it in at the <item> level.

Erik

Funny, my friend and I were just talking about this yesterday and comparing the American and Australian content advisory ratings for television.

The iTunes spec only mentions "explicit language or adult content" which is a bit vague compared to television ratings. In the U.S. television shows can be tagged for content containing violence, language, nudity, sexual content and rape ( http://en.wikipedia.org/wiki/Televisioncontent_rating_systems#Content_advisorysystem). In Australia there are also tags for drug use and horror or supernatural themes ( http://en.wikipedia.org/wiki/Televisioncontent_rating_systems#Consumeradvice).

Obviously video content has a broader range of what can be explicit than audio content, and the Explicit tag in iTunes originally started as a way of labeling music for sale in the iTunes store, the same way CD's have stickers in record stores, which is guided by the RIAA. Apple have published some information here: http://docs.info.apple.com/article.html?artnum=93031

Hope this helps,
Greg

Looks like iTunes grabbed the RIAA "standards" which are pretty vague:

Uniform Guidelines for Determining Whether a Sound Recording Should Use a PAL Notice

Participant record labels and/or artists should use the following guidelines to determine whether any particular sound recording contains strong language or depictions of violence, sex, or substance abuse to such an extent as to merit parental notification, as described in more detail in these Standards. Strong language or depictions of violence, sex, or substance abuse to such an extent is referred to herein as “PAL Content.” Only the record label or artist that owns and/or distributes the particular sound recording may determine whether the sound recording contains PAL Content and warrants the use of a PAL Notice.

A determination that a sound recording contains PAL Content is not a statement as to whether the sound recording is or is not suitable for particular listeners. Nor is the absence of any notification that a sound recording contains PAL Content a statement that the sound recording is completely devoid of all references to strong language or depictions of violence, sex, or substance abuse. Rather, it is utilized to ℹ provide parents, consumers, and companies within the sales or distribution chain notice that parental discretion is advised when purchasing the particular sound recording for children or when listening to the sound recording with children present; (ii) guide the labeling, marketing, and distribution of the sound recording; and (iii) provide notice whether an Edited Version (defined below) of a sound recording exists. A record label or artist determination that a sound recording contains PAL Content shall result in the use of PAL Content indicators, as more fully described in these Standards, to provide notice of the PAL Content. Such indicators are referred to herein as “PAL Notices.”

It is obviously not possible to define each individual situation in which a record label or artist should determine that a sound recording contains PAL Content. In making such a determination, however, record labels and artists should consider:

1. that contemporary cultural morals and standards should be used in determining whether parents or guardians would find the sound recording suitable for children;

2. the context in which the material is used, as some words, phrases, sounds, or descriptions might be offensive to parents if spotlighted or emphasized, but might not offend if merely part of the background or a minimal part of the lyrics;

3. the context of the artist performing the material, as well as the expectations of the artist’s audience;

4. that lyrics are often susceptible to varying interpretations, and that words can have different meanings and should not be viewed in isolation from the music that accompanies them (i.e., lyrics when accompanied by loud and raucous music can be perceived differently than the same lyrics when accompanied by soft and soothing music);

5. that such a determination requires sensitivity and common sense, and that context, frequency, and emphasis are obviously important; isolated or unintelligible references to certain material might be insufficient to warrant labeling a particular sound recording as containing PAL Content;

6. that these Standards apply to the case of a single track commercially released as well as to full albums (whether released in the form of a CD, cassette or any other configuration); and

7. that a sound recording may contain strong language or depictions of violence, sex, or substance abuse, yet due to other factors involved, may not merit a designation as containing PAL Content.

The record label or artist determination that a sound recording contains PAL Content shall affect the marketing, sale, and distribution of such sound recording, as described in greater detail throughout these Standards. For purposes of clarification, only the applicable record label or artist shall determine whether any particular sound recording contains PAL Content, and all other Participants shall abide by the applicable record label or artist’s determination.


Erik