An air is a light melody. As Wikipedia informs us,
Lute ayres emerged in the court of Elizabeth I of England toward the end of the 16th century and enjoyed considerable popularity until the 1620s. Probably based on Italian monody and Frenchair de cour, they were solo songs, occasionally with more (usually three) parts, accompanied on a lute. Their popularity began with the publication of John Dowland's (1563-1626) First Booke of Songs or Ayres (1597). His most famous ayres include Come again, Flow my tears, I saw my Lady weepe, and In darkness let me dwell.But look for no Dowland influence in this air. It is just a charming tune. But I was fascinated with sudden harmonic shifts at the time so there is a lot of that.