What is a P?

Besides a miserable pile bad samples?

Lately, the tag has been often added, or even self added to end of user names. Since I am a bit involved in the world of VOCALOID, I thought I would look into exactly what a "P," or producer is considered in Japan. Yes, I realize I am rather late to the party, but better late than never, right?

The following are considered a producer in Japan.

1. Someone that leads projects dealing with television programs, music, advertisement, games, and etc.
2. The main character in the game THE IDOLM@STER.
3. An individual that creates and upload their original projects to NicoNicoDouga; usually related to VOCALOID.
4. Tsuchiya Toshio from the Japanese variety show "Denpa Shounen Series" is usually called "Tproducer."
5. A character from the game Weekly Toro Station is called Producer.

Japan's Broadcasting industry

A producer is the chief executive of a TV or radio show. A producer has his hands in all things from: attending meetings, working with budgets, negotiating with stars and sponsors, arranging schedules and overseeing actual production. They have control of each director's progress/edits and the final say when decision.s are made. There may be a Chief Producer above the producer  who brings everyone together. Also, the producer may also work as the Chief Director at the center of a variety TV station. For anime, there are times where the producer and supervisor may be separate people.

NicoNicoDouga

Someone that creates or uploads content could be called a "～P." The P stands for producer. Since player that you control in the game THE IDOLM@STER was called "(name)P," the tag was adopted to differentiate between contributers (there were many community videos and PVs at first as the community for creating such content was so small). It was used for people that made songs with VOCALOID or UTAU, or videos with MikuMikuDance. The first person that was christened as a "P" was probably OneCupP (ワンカップP) in 2007. However, the tag still wasn't broadly used until several months after. For a time, the tag either was not added to a contributers name, or added later but still saw little use (producers like OSTER project, ika, kz, or ryo for example）.

The P can be added by the uploader or by other people considered producers. If the "P" isn't added by the creator, there are times where the viewers can add P to the uploader's name in the tags. It can also be added to someone if their name was written in the creator's comments or video explanation and they uploaded several videos.

To the general public, a producer the the production boss. But in THE IDOLM@STER, it was more of a manager or trainer of sorts. Today, 「～P」 is close to a title that you could give someone that is the head of a company section in Japan and thus follows the same rules as other honorifics in Japan (In other words, "～P-San" sounds weird).

Source: 
http://tinyurl.com/78x37n 
http://tinyurl.com/d5j5lxo