org-refile-targets

org-refile-targets is a variable defined in `org.el'.
Its value is

nil

Documentation:
Targets for refiling entries with M-x org-refile.
This is a list of cons cells. Each cell contains:
- a specification of the files to be considered, either a list of files,
or a symbol whose function or variable value will be used to retrieve
a file name or a list of file names. If you use `org-agenda-files' for
that, all agenda files will be scanned for targets. Nil means consider
headings in the current buffer.
- A specification of how to find candidate refile targets. This may be
any of:
- a cons cell (:tag . "TAG") to identify refile targets by a tag.
This tag has to be present in all target headlines, inheritance will
not be considered.
- a cons cell (:todo . "KEYWORD") to identify refile targets by
todo keyword.
- a cons cell (:regexp . "REGEXP") with a regular expression matching
headlines that are refiling targets.
- a cons cell (:level . N). Any headline of level N is considered a target.
Note that, when `org-odd-levels-only' is set, level corresponds to
order in hierarchy, not to the number of stars.
- a cons cell (:maxlevel . N). Any headline with level <= N is a target.
Note that, when `org-odd-levels-only' is set, level corresponds to
order in hierarchy, not to the number of stars.

Each element of this list generates a set of possible targets.
The union of these sets is presented (with completion) to
the user by `org-refile'.

You can set the variable `org-refile-target-verify-function' to a function
to verify each headline found by the simple criteria above.

When this variable is nil, all top-level headlines in the current buffer
are used, equivalent to the value `((nil . (:level . 1))'.

You can customize this variable.