A soloist is a musician who performs alone, or who plays or sings the special part that stands out from the rest of the group. Two slightly different pictures live inside this one word. Sometimes the soloist really is alone on the stage — one person, one piano, no one else. But more often the soloist is standing in front of a whole orchestra or choir. Everyone plays, and one person plays the part everyone is listening to. That second use is the common one in classical music: the violin soloist has an orchestra of sixty people behind her, so she is not alone at all, and we still call her the soloist. The word also covers singers, so you can be a soloist in a choir — the one member who sings a few lines by herself while the others rest or hum quietly. In a jazz band, when one player takes a solo for a while and the others keep the rhythm going, we usually say 'he's taking a solo' rather than calling him the soloist; 'soloist' feels more classical, more like a printed concert programme. It is a neutral, slightly formal word — you would see it on a poster or in a newspaper review, not usually in casual conversation. And it carries a little weight: calling someone a soloist suggests they are good enough to be trusted alone, which is why musicians say things like 'she's a soloist now' with a bit of pride.