What is 'The Willow Song' about in the Shakespeare play Othello?

I'm not sure what the song is literally about, but it's used as foreshadowing in Othello. Desdemona, just before she is killed by Othello on her Deathbed, is speaking to Emilia about a song her maid sang when Desdemona was a child just before the maid died (murdered, I believe) and thus it implies, when she sings it, that desdemona is too going to be murdered too as she has sung the song.