Arioso means airy. In musical terminology, arioso is a type of solo vocal piece which would occur in an opera. Arioso is a composition that is close to those of speech, like reciting a poem but not leaning on repetitive pattern. Although it is originally a vocal form, the term arioso was extended to instrumental compositions of the same melodic character. One of the most famous instrumental ariosos was composed by Johann Sebastian Bach, and serves as the sinfonia of his cantata, Ich steh mit einem Fuß im Grabe, BWV 156, as well as the middle movement of the Harpsichord Concerto, BWV 1056.
Oh, right, for those of you who are curious what BWV is, BWV stands for Bach- Werke-Verzeichnis or Bach Works Catalogue. BWV followed by the work’s number does not show chronology but thematic.