1.66:1 means the horizontal is 1.66 times as long as the vertical.
It is a fairly common aspect ratio. Most Disney animated movies for example are made in 1.66:1 aspect ratio.
It can be anamorphic.
As far as DVDs go, anamorphic means that the encoded image is 1.78:1 or 16:9. For 1.85:1 films that requires a small black bar to be added to the top and bottom of the image, for 1.66:1 films it requires a small black bar to be added to the sides of the image. Not sure if the particular DVD you are asking about is anamorphic though. Sorry.
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