what does “Warning--entry type for ”…“ isn't style-file defined” mean?

Question

After switching to the classicthesis template for a compilation of class notes I took last term, I'm now seeing warnings like:

Warning--entry type for "wiki:curvature" isn't style-file defined
--line 638 of file myrefs.bib

Here's the bib entry for the warning above:

@webpage{ wiki:curvature,
   author = "Wikipedia",
   title = "Curvature --- Wikipedia{,} The Free Encyclopedia",
   year = "2012",
   url = "http://en.wikipedia.org/w/index.php?title=Curvature&oldid=488021394",
   note = "[Online; accessed 25-April-2012]"
 }

the classicthesis bib section looks like so:

\bibliographystyle{plainnat}
\label{app:bibliography}
\bibliography{myrefs}

First question is what does this style defined warning mean? Second question, presuming this is worth fixing, is how would it be fixed (one way to do so would be to revert to the unsrturl.bst instead of plainnat as used by classicthesis).

Answer 1

It means that @webpage is not a recognized type by the BibTeX style plainnat. So your entry is probably not formatted or only formatted in a very simple way (I have to check).

Update

I found a copy of the bibTeX source on some old disk ... and there it says:

The |built_in| function {.{call.type\$}} executes the function specified in |type_list| for this entry unless it's |undefined|, in which case it executes the default function .{default.type} defined in the .{.bst} file, or unless it's |empty|, in which case it does nothing.

So now looking into plainnat.bst we find

FUNCTION {default.type} { misc }

which its what we saw. So basically, if you are fine with @misc as a type, then you don't need to do anything really (and it is probably the only type that fits a webpage being referenced). If you want to get rid of the warning you could change to @misc (or some other standard type).