"Ave Verum" is considered by many to be William Byrd's finest work. It was first published in volume one of his Gradualia in 1605.
The verse itself is from a 14th century handwritten document from Reichenau, penned by an unknown author.
See my translation of Mozart's Ave Verum.
The final lines of the Byrd Ave Verum, "O Dulcis, O pie, O Jesu fili Mariae, miserere mei" mean "O sweet, O merciful, O Jesus, Son of Mary, have mercy upon me."
Here are midi (computer music) files for you to download and listen to (If you're using Microsoft Windows, simply click on the link and they should play automatically. If you're not using Windows, I'm going out on a limb and assuming you're technically competent enough to figure things out for yourself....).
Also note that there are midi files of each individual voice part for each piece, so you can hear what each one sounds like - especially your own!
These midi files should give you a fair idea of what each piece - and each individual voice part - sounds like, especially if you're unfamiliar with reading music.
And for those that would like to dowload a viewable and/or printable copy of the score (HINT: most people will want the PDF file; don't try to view the Postscript file unless you know what you're doing):