The GNU Lesser General Public License is a software license designed as a compromise between the GNU General Public License and simple permissive licenses such as the BSD license and the MIT License.
It places a copyleft restriction on individual source code files but does not copyleft the program as a whole provided you use "a suitable shared library mechanism for linking" and follow certain other restrictions. The license is only useful for software libraries; it was once called the GNU Library General Public License.
The main difference between the GPL and the LGPL is that the latter can be linked to a non-(L)GPLed software program.
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