A virtuoso is someone (usually in the performing arts) who is an expert in his or her field.
A musical virtuoso is one who plays a musical instrument very well. Musicians who have exceptional talent and can play extremely fast and difficult music are "virtuosi" (plural of "virtuoso"). In the 19th century Niccolò Paganini was a virtuoso violinist as well as a composer. Franz Liszt was a virtuoso pianist and composer.
Musicians may sometimes talk about “virtuoso music” meaning music which is so difficult that only a virtuoso could play it.