As an explanation, I am fairly certain this is correct. Whether or not this is what we would actually call it in English, I am slightly less certain! Hence CL3

See:
http://de.wikipedia.org/wiki/Schnittverzierung#Farbschnitte

"Naturschnitt" explained in article

It means that the edges of the pages are not decorated (e.g. gold edging or blue like a Langenscheidt dictionary).

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Note added at 19 mins (2011-04-01 12:16:57 GMT)
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Also called "Weißschnitt" in German and definitely refers to the colo(u)r of the edges of the pages, rather than the way the paper has been cut.

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Note added at 26 mins (2011-04-01 12:24:18 GMT)
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plain edge(d) pages

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Note added at 28 mins (2011-04-01 12:25:46 GMT)
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... January to December
8 AM to 7 PM schedule
Monthly tab
64g, acid-free paper
Plain edge pages
Tear-off corner opens to day in progress
Sewn binding, ...
http://www.dealtime.com/diaries-with-lock organizer-and-plan...

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Note added at 39 mins (2011-04-01 12:36:50 GMT)
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all edges plain
is another possible variant that gets a number of ghits from specialist book dealers.