org-refile-use-outline-path

org-refile-use-outline-path is a variable defined in `org.el'.
Its value is

nil

Documentation:
Non-nil means provide refile targets as paths.
So a level 3 headline will be available as level1/level2/level3.

When the value is `file', also include the file name (without directory)
into the path. In this case, you can also stop the completion after
the file name, to get entries inserted as top level in the file.

When `full-file-path', include the full file path.

You can customize this variable.