Vocaloid Fanmade Promotion Video, which is commonly abbreviated to Fanmade PV, is a short film or video made by fans of the vocaloid original work, not by the original creator, and accompanying of the work sung by vocaloid (including cover). Promotion video(PV) is a term often used in Japanese and it is what is called music video(MV), music clip or video clip in English. They can be considered similar to MAD/AMV (movie anime dojinshi/anime music video) works, and some PVs even claim to be these.
Various great vocaloid fanmade PVs have been made and uploaded on video-sharing sites, such as Nico Nico Douga or Youtube, to support original works/videos/songs from which they derived. Most vocaloid fanmade PV creators use CG works, their own hand writing pictures, photographs or live-action films to create them. As relatively few PVs are completely animated, the false etymology of "picture video" has entered some parts of the English-speaking fandom.
Vocaloid fanmade PVs are beloved by many people and sometimes they are mistaken for their original works when they become very famous and popular.
Since vocaloid fanmade PVs are offsprings of the original works/videos/songs which are often called 本家(honke/the original) in Japanese, they are regarded as a kind of derivations of those originals just like fanfiction. 
Effects of Vocaloid Fanmade PVs Edit
Vocaloid fanmade PVs frequently make the original works more attractive with their renderings and arts, and also they can make a much wider audience aware of the originals. The most viewed vocaloid fanmade PV on Nico nico video is 「3DみくみくPV♪(3D Miku Miku PV)」Nico Video broadcast YouTube broadcast which accompanies of 「みくみくにしてあげる♪(Miku Miku ni Shite Ageru)」 sung by Miku Hatsune. It was viewed more than 2,330,000 times as of May 30th, 2010.
However, while those splendid PVs can make the original works more popular, it must be noted that what vocaloid fanmade PVs show are not always faithful to the original works/videos/songs or the original authors’ intents, for they are created with each fanmade PV creator’s own intention. Some PV creators make travesties of the original works and quite a few PV creators depict their own stories and settings which are unspecified in the original videos/songs with free interpretations and imaginations of their own; in some of those fanmade PVs, what they depict are completely different from what the songs mean. Though the fact itself does not take away from the value of them, it is one of the reasons why they often invite misunderstandings among fans and make fans clash with each other over how to interpret the songs.