In just three short lines, this haiku-like poem sets up a small, quiet scene. A man imagines, or perhaps knows, that his wife and daughter dance together while he is not there. The poem doesn't say where he is or why he's gone, so we only have the image and the feeling around it.
The opening line, "wind off the water," gives the poem its air and movement. It could be the place where he is, or the place he pictures them. Either way, the wind feels like the dance: light, moving, a little out of reach.
The speaker seems both warm and wistful. He takes pleasure in the picture of the two people he loves enjoying themselves, but the phrase "when I am away" admits he is missing it. The title, "Party of two," sharpens that feeling, since he is not the third guest. The mood is tender and gently lonely, with joy that he can only watch from a distance in his mind.