GNU GPL #
The license under which the WordPress software is released is the GPLv2 (or later) from the Free Software Foundation. A copy of the license is included with every copy of WordPress, but you can also read the text of the license here.
Third Party Libraries #
Third-Party libraries must be GPLv2 compatible, but retain their own copyright.
Contributor Copyright #
As a contributor, you retain the copyright to your code, however by submitting it to trac you are releasing it under the GPLv2.
For the GPL bit, can probably pull text directly from http://wordpress.org/about/license/
If you want to link up all the Third party libraries, I’d assume you can just yank that from the .org api pull in the credits screen too.
Making it so.