An "utaite", in the Vocaloid fandom, is the name that is given to people who cover popular songs.
Utaite is short for Uttatamita. I believe Uttatemita means something, like "I sing," in Japanese. They're also called Nico Nico singers. They're people who sing covers of popular songs, & upload them onto Nico Nico Douga. The majority of the songs covered are Vocaloid songs. .