I'm not kidding about the plural "datums" it seems peculiar to surveying, and I'm dithering over how best to note this. In the mean time here's an Introduction to Geodetic Datums by by Peter H. Dana, Department of Geography, University of Texas at Austin, 1995.
Note that this usage is countable, in contrast to the usually derided (yet overwhelmingly prevalent) uncountable usages such as "this data shows ..." -dmh 02:26, 14 Apr 2005 (UTC)
A definition must identify a phenomenon without errors of inclusion or exclusion, and be as intrinsic as possible. The term datum must not be take as an appendix to information, since it composes the concept of information and, as such, cannot be taken as the whole, while being a part of it.
- A definition on Wiktionary must be written in grammatically correct English, and ideally should be understandable. A definition that cannot be understood has no value as a definition. --EncycloPetey 08:03, 21 November 2007 (UTC)