Orphaned packages have no active maintainer.  

Orphaned packages remain in the main CRAN packages section as long as
they pass "R CMD check" for the current release version of R.

Everybody is more than welcome to take over as maintainer of an orphaned
package.  Simply download the package sources, make changes if necessary
(respecting original author and license!) and resubmit the package to
CRAN with your name as maintainer in the DESCRIPTION file of the
package.

Possible reasons for orphanizing a package:

1) The current maintainer actively wants to orphanize the package,
   e.g., due to no longer having time or interest to act as package
   maintainer.

2) Emails sent to the current maintainer by the CRAN admins bounced, or
   were not answered for longer periods of time.

The new orphanizing process since 2011-08-01:

1) The package gets the special keyword "ORPHANED" as maintainer in
   the DESCRIPTION file, and the package sources and binaries are
   updated on CRAN without increasing the version number

2) If the package cleanly passes R CMD check for the current release
   version of R, it remains in CRAN's src/contrib directory.  Otherwise,
   it is moved to the Archive.

3) File PACKAGES.in in CRAN's src/contrib directory (the repository
   package metadata file) provides information about the original
   maintainer, and the date and reason for orphanizing.

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The old orphanizing process:

1) The package gets the special keyword "ORPHANED" as maintainer in
   the DESCRIPTION file, the patch level of the version number is
   increased.

2) If the package cleanly passes R CMD check for the current release
   version of R, it remains in CRAN's src/contrib directory.  Otherwise,
   it is moved to the Archive.

3) File PACKAGES.csv in CRAN's src/contrib/Orphaned directory shows the
   date when the package was orphaned and the release version of R at
   that point in time.