Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The zlib License is a permissive free software license which defines the terms under which the zlib and libpng software libraries can be distributed. It is also used by other free software packages, e.g., on SourceForge.The zlib License has been approved by the Free Software Foundation (FSF) as a free software licence,and by the Open Source Initiative (OSI) as an open source license. It is compatible with the GNU General Public License.