What is a swap file?
unix, vi
Solution
From the Vim documentation:
Vim stores the things you changed in a swap file. Using the original file you started from plus the swap file you can mostly recover your work.
The documentation also describes the recovery procedure in case you need it.
Problem
Using vi I started editing a html file and I accidentally exited out of session, now when I try to edit the file again I receive this message : E325: ATTENTION Found a swap file by the name ".myfile.swp" While opening file "myfile.html" dated: Tue Jul 3 09:55:39 2012 (1) Another program may be editing the same file. If this is the case, be careful not to end up with two different instances of the same file when making changes. Quit, or continue with caution. (2) An edit session for this file crashed. If this is the case, use ":recover" or "vim -r myfile.html" to recover the changes (see ":help recovery"). If you did this already, delete the swap file ".myfile.html.swp" to avoid this message. Swap file ".myfile.html.swp" already exists! Has any damage occured to myfile.html ? What I think is occuring is that its storing a copy of the opened file when I exited my session (the swap file) ?