I opened a discussion in the main Forum about the current entry we have about J-Rock, as it is wrong and unclear (and contradicts the also not-that-great entry about Group Sounds)
J-Rock
"Japanese rock (Japanese: 日本のロック, Hepburn: Nihon no Rokku), sometimes abbreviated to J-rock (ジェイ・ロック, Jei Rokku), is rock music from Japan. Influenced by American and British rock of the 1960s, the first rock bands in Japan performed what is called Group Sounds, with lyrics almost exclusively in English. Folk rock band Happy End in the early 1970s are credited as the first to sing rock music in the Japanese language. Punk rock bands Boøwy and The Blue Hearts and hard rock/heavy metal groups X Japan and B'z led Japanese rock in the late 1980s and early 1990s by achieving major mainstream success."
Group Sounds
"Predating J-Rock, Group Sounds is generally a blend of Kayōkyoku, Garage Rock, and Beat music. sung in either English or Japanese."
GS was founded around 1963 - 64, at the start of Beatlemania, and exploded into popularity in 1966, following the Beatles performance at the Budokan Arena."
In Japan it was only used around the early '90s as a catch-all term, then not too much later on, right?
Actually overseas it is a bit different, as it is used to differentiate those rock (and often pop rock) bands that have a distinctively Japanese sound, both ones like L'Arc~en~Ciel, GLAY or Luna Sea, that came from the vk scene, toning down their music for the mainstream and the ones like... Asian Kung-Fu Generation or The Oral Cigarettes for example, that also play music that does not really fit into any specific sub-genre and is typically Japanese. It is really interesting that overseas many use the term for a long, long while, they all know what they mean, what bands do and do not fit into the category (more or less), but I never came across any sources that would have a clear definition of what it is. What is certain is that when I first encountered it around 2000 it was already a commonly used term within the (then very small) international Japanese music fanbase, with a site called J-Rock Channel" being one of the centers of the online subculture.