MADs

An iM@S MAD (The iDOLM@STER MAD) is a MAD movie created by editing videos from the game The iDOLM@STER. A "MAD Movie" is a Japanese fan-made video consisting of multiple videos, known elsewhere as Anime Music Videos (AMV).
As soon as various people uploaded their play videos of the game, iM@S MADs broke out in Nico Nico Douga, the most popular video sharing website in Japan. One after another, these iM@S MADs became a tower of masterpieces. Many viewers on Nico Nico Douga frantically began to devour the iM@S MADs. They were not satisfied by just sharing videos. They wanted to create and provide their own music videos. Combining the original iM@S videos with every music they can use, along with extraordinary editing skills, iM@S videos have evolved in such a short time.

From The iDOLM@STER MAD World Service. Full credit to the contributors.