Hatsune Miku is a JPop artist. Like any JPop artist she releases songs and performs concerts. The only difference is that she's not human — she's a Vocaloid.
Her Vocaloid (human voice synthesis software) was released by Crypton Future Media in 2007. Anyone who licenses the software can use her voice to produce music.
Major record labels such as Victor Entertainment and Sony Music Japan have released Hatsune Miku songs. Fans of Hatsune Miku have also produced popular songs and videos featuring her.
The Kanji of Hatsune Miku's (初音未来) name can be translated as "first future sound". She's the first virtual pop artist to be commercially successful.
Hatsune Miku has become a Japanese pop culture sensation.
She's featured in cartoons and commercials. She also has a popular line of figurines and toys.