obangya
オバンギャ

n : An older, more experienced fan

ofi
オフィ

n : A band's official website

okimo
オキモ

n : A fan who is considered gross by other fans

okini
オキニ

n : A fan who is liked by other fans or a certain band member

okira
オキラ

n : A fan who is hated by other fans or a certain band member

ongen
音源

n : CDs, cassettes, MP3s; anything you listen to music on

ongen fan
音源ファン

n : A fan who only listens to a band, rather than go to concerts

ongen ota
音源ヲタ

n : Same as ongen fan

onnagata
女形

n : An effeminate or female-looking band member

ooei
OA

n : Opening act. The first band to play at an event. Usually not listed as an OA unless the band is an invitee by another band
also written: オープニングアクト(oopuningu akuto)

oshare kei
おしゃれ系

n : lit. "fashionable style" - Bands that have more upbeat and colorful music, with the fashion sense to match. Tend to be more jazzy and pop. Due to the stigma of oshare, many bands are choosing to be more koteosa. Examples: AnCafe, Charlotte, Shelly Trip Realize
also written: お洒落系(oshare kei), オサレ系(osare kei)

otsu

Short for "otsukare-sama" which means "great job" or "thanks"