Visiting Japan and talk to people, one can always learn some fresh vocabulary. This time, the first such word to me is this one. I am sure that the English word which it represents does not communicate with most English speakers. In truth, it refers to "voice over". More specifically, it indicates a type of passionate practice by people who dreams to become a radio actor to practice their skills by applying their voice to existing anime pictures.
It seems that there is a word which has a longer history in this context. That word is プリレコ or pre-recording. It is a way to produce motion pictures by preparing the voice part first. In fact, I have used プリレコ method many times to create my own short presentations, and found out that it is rather easy and convenient.