Redmine

RAILS_ROOT is the folder which contains all of redmine's code. When you extract the zip/tar.gz you've downloaded to a folder, that folder location is the effective RAILS_ROOT for that application (which is in this case redmine).

For example, if you were to create /home/redmine and put all the zip content into it, then /home/redmine is your RAILS_ROOT.

In the case mentioned in the documentation, this step is to copy old files to the new install.

Thanks Tom. I think the page should replace "RAILS_ROOT/files directory content" with "files/ directory content" to be consistent with steps 2 and 3