The GNU General Public License is a free, copyleft license for software and other kinds of works. The Free Software Foundation (FSF) has released GNU General Public License version 3 (GNU GPL). The GNU GPL is the most widely used free software license worldwide and claims that almost three quarters of all free software packages are distributed under this license.
Richard Stallman released the Version 1 in 1989, and version 2 in 1991. However, with increasing use of free software, changing computing practices and new threats, the release of version 3 became necessary to address free software issues in the current computing scenario. You can read the GNU General Public License Version 3 now and how it guarantees your freedom to share and change all versions of a program and make sure it remains free software for all its users.
Why Upgrade to GPLv3 is an interesting article that explains that upgrading is a choice. GPL version 2 will remain a valid license, however and no disaster will happen if some programs remain under GPLv2 while others advance to GPLv3. The reason to upgrade the licences is to deal with the existing problems which GPLv3 will address like tivoization, Digital Restrictions Management, and patent protection issues. Better internationalization, gentler termination, support for BitTorrent, and compatibility with the Apache license are more reasons to upgrade.
Also upgraded is the GNU Lesser General Public License that incorporates the terms and conditions of version 3 of the GNU General Public License, supplemented by the additional permissions.