pronoun
A katakana rendering of the second-person pronoun 'you'. In Japanese it sounds foreign, playful, or affected, so ordinary speech more often uses a name, title, or pronouns such as あなた, 君, or お前 depending on the relationship.
ユー、次は何を歌うの？
You, what are you going to sing next?
彼はふざけて私を「ユー」と呼んだ。
He jokingly called me 'you.'