A style of Japanese music that really has nothing to do with music. Visual Kei (VK) bands are generally rock or indies bands that dress in different types of elaborate outfits. Many conservatives shy away from VK bands because the men often wear heavy makeup and costumes that make them look like women. Basically VK = crossdressing Japanese rockers.
Vk bands dress in a feminine manner but can have many styles. Malice Mizer had more of a romantic/gothic/1800's feel whereas Dir en grey had a more of a slutty, vinyl miniskirts and thigh-high bitch boots style. Kagrra does more traditional clothing like colorful kimonos and Psycho le Cemu is just plain messed up with schoolgirl uniforms and outfits that look like cheap halloween costumes.
VK rockers are generally NOT gay/bisexual. They dress like women to attract record deals, attention, and fans, however, after signing a major record deal and going "mainstream" they usually lose the visual look and become "normal".
Dir en grey used to be a visual kei band becuase they dressed like women with heavy makeup, crazy hair, and feminine clothing.