Why does the professor say this:

W: The term "Baroque" refers to a style and a culture rather than a precise period in history．Architecture, painting, and music each have a style called Baroque．One of the most striking features of the Baroque style is its expressiveness．Baroque music is a vigorous style combining imagination with great feeling．There’s great use of dissonance to express extremes of emotion, especially in vocal music．And compared to Renaissance music, Baroque music has more ornament．Trills and grace notes-little twists on notes-all find their way into musical notation．Baroque music is known for its virtuoso instrumental music．Instrumental music had been gaining in importance and came into its own around 1600．Music was freed from the necessity of words, and it now moved to dance rhythms rather than speech rhythms．The new style demanded new musical forms．It was in the Baroque era that some of the forms we know today began to take shape: the opera, the sonata, and the concerto．The person generally given credit for inaugurating the Baroque style was Claudio Monteverdi．Monteverdi’s career took place at the same time as other developments, like the rise of solo singing and, urn, experiments to re-create Greek music and drama．These experiments led to a new form called opera．Monteverdi was the first of the great Italian opera composers, and he was also the first to explore the tone colors of the orchestra．Monteverdi was a revolutionary．He took musical risks, like doing exciting things with rhythms, and using dissonance to make the music more expressive．The golden age of Baroque instrumental music began with orchestral combinations like the one Monteverdi used in his opera Orfeo．The orchestra for Orfeo consisted of two harpsichords, two contrabasses, twelve members of the violin family, a double harp, two pipe organs, four trombones, two cornets, a small flute, three muted trumpets, and an assortment of other instruments．With these instruments, Monteverdi told the Greek legend of Orpheus．The instruments dramatized the story’s characters and plot．For example, the high flute and a small violin accompanied the shepherd, brasses and organ music suggested the underworld, and so forth．Orfeo was full of expressive devices, and demanded masterful playing from strings and brass, as well as virtuoso singing.
M: Excuse me, Professor Stevens．Could you explain exactly what "virtuoso" means?
W: Sure．"Virtuoso" is an Italian word．It means highly skilled or ..．worthy．A virtuoso piece of music requires a highly skilled vocalist or a masterful player.
M: But a person can be a virtuoso, right? I mean, we can say, for example, "He’s a real virtuoso."
W: Yes, that’s right．A virtuoso is a musician who plays with great skill and technique, or who has an extraordinary individual style．It was the, urn, violin virtuosos who perfected new forms of instrumental music in the Baroque period．All of the great violinmakers of the time were concentrated in Italy．The terms "concerto" and "sonata" also come from Italian．The concerto and the sonata developed as vehicles for virtuoso musicians to show off their skills．The concerto became the dominant instrumental form of the Baroque period．Concertos feature solo instruments-usually violins-and orchestra, or they can feature groups of instruments and orchestra．The music is characterized by its dazzling virtuosity and ornamentation．Baroque concertos required a lot of technical skill-in both the composing and the performing．The most famous of all Baroque concertos were for solo violin and orchestra．Vivaldi’s Four Seasons are probably the best known examples．The Four Seasons are four related concertos-one for each season．They are pure, quintessential Baroque music- descriptive, expressive, elaborate-and with virtuoso violin playing．Before I go on, let’s pause here so we can listen to the first of The Four Seasons．Here is "Concerto Number 1, Spring."