On an International passport, what does TYPE P mean?

This is one of those Homer Simpson moments - P is for Passport (doh!) as opposed to any other kind of identity document. It is an ICAO requirement for machine-readable passports that "Type P" appears on the machine-readable page. The actual specification for machine-readable passports is very detailed as there is no point in them unless every country can easily read every other country's passports by machine - it's in the first document downloadable from http://www2.icao.int/en/MRTD/Downloads/Forms/AllItems.aspx?RootFolder=%2fen%2fMRTD%2fDownloads%2fDoc%209303%2fDoc%209303%20English&FolderCTID=&View=%7bC6E1DF57%2d954A%2d4BCF%2dBF58%2dD7D58D9F1FB5%7d Countries may differentiate different types of passports (such as diplomatic passports, or refugee travel documents) by adding another letter after P if they wish. A passport card as opposed to a passport book would be an IP. Germany produces its own national identity cards in a format which follows that for machine-readable passports as they can be used instead of a passport to travel to other European Union countries, and these are type ID. It's because there are occasions when a passport is not necessarily required for international travel that the "type" matters.

Each passport has a data page and a signature page. A data page has a visual zone and a machine-readable zone. The visual zone has a digitized photograph of the passport holder, data about the passport, and data about the passport holder: Photograph Type [of document, which is "P" for "passport"] Code [of the issuing country, which is "USA" for "United States of America"] Passport No. Surname Given Name(s) Nationality [which is "United States of America"] Date of Birth Place of Birth (lists only the state followed by "USA" for those born in the United States; lists the country of birth for those outside the US) Sex Date of Issue Date of Expiration Authority Endorsements