1)  A late 16th- and early 17th-century type of English song.  It was primarily a solo song accompanied by the lute (occasionally the virginal), often with the lowest part doubled by a bass viol.  In many cases the composers provided for an alternative vocal accompaniment, printed separately on the opposite page so that the parts could be read simultaneously by three singers seated.  The ayres range from serious songs, often through-composed, to light and gay tunes, usually strophic.

2)  In the 17th century, a movement of a suite.

3)  English writers of the 17th century use the term ayre (aire) in the sense of key or mode.