If you have in your code \bibliographystyle{plainnat} then the "URL" text comes from the style.
In the plainnat.bst file you can find the following code:
FUNCTION {format.url}
{ url empty$
{ "" }
{ new.block "URL \url{" url * "}" * }
if$
}
The part "URL \url{" url * "}" * is responsible for your problem. You can delete URL at the start of it or change it in any way you like.
For the urldate (it is a little more complicated):
In the same plainnat.bst file for example under the code above add the following lines:
FUNCTION {format.urldate}
{ urldate empty$
{ "" }
{new.block "[Accessed on: " urldate * "]" * }
if$
}
Save it and do a search in the same file for "url". In one place you will find:
ENTRY
{ address
author
........%some more functions
type
url
volume
year
}
Add urldate under url. Save it. Then do a search for format.url output and add under every single one format.urldate output.
For example by misc:
FUNCTION {misc}
{ output.bibitem
format.authors output
author format.key output
title howpublished new.block.checkb
format.title output
howpublished new.block.checka
howpublished output
format.date output
format.issn output
format.url output
note output
format.urldate output %places the "urldate" after the "note"
new.block
fin.entry
empty.misc.check
}
So, the order of the different outputs (e.g. format.urldate output) in the different functions (e.g. misc) denotes also the order of their insertion in the references.
That is all :)
natbibpackage, but by the bibliography style you employ. The bibliography style also determines what may (or may not) be done with fields such asurldate. In short: Which bibliography style do you use? – Mico Mar 18 '13 at 18:05