.svn

can anyone tell me what the directory /.svn means as I am not sure what it is or whether I should delete it.

You would find that folder next to a folder and file structure that is linked to a subversion repository,

http://en.wikipedia.org/wiki/Apache_Subversion

The .svn files are used by the versioning software (for example Tortoise SVN) to track the revision state of the files in that folder.

Zen Cart files should not have those in there: there is no repository to link to.

Deleting them will not break the ZC site but break the link to the repository.

is it likely that it will affect wordpress, google froogle, any of the payment modules etc
PS I have no idea what turtle is.

Its is also in the admin folder

It sounds like the person who took care of the site before you used subversion to manage their version control. There's no harm in deleting these files or leaving them there as long as you don't plan to use Subversion (and it sounds like you don't plan to).

I've always looked after the site. I created it.
Version Zen Cart 1.3.8a

Patch: 1::

Database Patch Level: 1.3.8

I have twitter, facebook and wordpress installed.