Loituma is a quartet from Finland who rose to popularity in their homeland as folk music singers and for their use of traditional instruments, mostly the kantele, or Finnish zither.
The group is famous among anime fans after their song "Ievan Polkka," particularly its gibberish part, was used in a flash animation involving Inoue Orihime of "Bleach" twirling a leek, or a spring onion, on her right hand while holding a bag of groceries on the left. The animation became an internet meme by the names "Loituma Girl" and "Leekspin". "Levan Polkka" is a common misreading of the song title, and has further spawned such variations as "Leva's Polka".
Most of the posts with this tag do not reference the band itself but the flash animation. The original: post #38012.
An important later development was the Hatsune Miku version of the "Ievan Polkka" gibberish. It was one of the earliest Miku memes and established Orihime's leek as a part of Hatsune Miku's (and Hachune Miku's) basic equipment in fan art.