MMD is an abbreviation for Miku Miku Dance which is a free 3D modeling and animation software based around vocaloids and Hatsune Miku. It started out really simple but has now become quite the beast. Read about it in english at MMD wiki. Software much like MMD: RinRinDance & iSTDance.
MMD-cup 5
The MMD-cup lets you vote for the best miku miku dance video. If you like a video, add it to your mylist! The contest is right now in its preparation stage and will open in a couple of weeks. People that make MMD videos know the theme and are preparing for the big onslaught of uploaded videos tagged with 第5回MMD杯.
Theme
The theme for MMD-cup V is, as you can see in the video above, 1:「変」 2:「祭」 3:「想」. (Read them in what ever order or however you want).
Note that the voting will begin the 20th of august.