Most likely means an AVI with video encoded in xvid and audio encoded in AC3.
If in doubt, use
gspot,
avicodec, or similar tools.
This is my preferred way of playing those on a PC:
Get xvid
here, and play the file with
Media Player Classic.
If you don’t like MPC, but prefer Windows Media Player, you can download and install the
AC3 filter instead.
If you don’t like any of the above you can play the whole thing with
VideoLan.