Final answer:
An arioso is a style of vocal music that is more melodious than recitative but less elaborate than an aria, accompanied by instruments, and represents an evolutionary step in Renaissance vocal music.
Step-by-step explanation:
A arioso is a melodic recitative that is accompanied by instruments. This term describes a style of solo opera singing between a fully composed aria and a more speech-like recitative. Arioso is typically more melodic than a recitative but less elaborate than an aria. In the context of music history, especially considering the musical developments during the Renaissance, arioso signifies an important aspect of the evolution of vocal music. As composers moved away from the medieval tradition, which emphasized more austere forms of chant, they began to embrace more expressive forms like the arioso that allowed the natural rhythm of the text to be enhanced by melody, and this was supported by instrumental accompaniment such as the basso continuo.
Composers of the Renaissance and Baroque periods experimented with polyphony and more complex harmonies, including more frequent use of intervals like the third. Madrigals and motets were significant genres of this era, and they were sometimes accompanied by instruments, which underscores the variety of vocal and instrumental interactions typical in early music, similar to the interplay found between the voice and accompaniment in an arioso.