A skylark is a small brown bird that sings while it flies high in the open sky, especially over fields. You often cannot see it easily, but you can hear the song pouring down. The name is sky + lark: a lark of the sky. (A lark is a kind of songbird.) In Britain it is a countryside bird people know from walks and from poems; it is not a cage bird. Though actually the same spelling is also a verb, a little old-fashioned: to skylark means to play around and not be serious, especially when you should be working. Sailors were using it that way by 1809, and it may have mixed with an older northern word lake or laik, 'to play,' from Old Norse. So a skylark in a poem is a bird; 'Stop skylarking!' from a ship's officer means 'Stop fooling about!'