GNU Lesser General Public License: Meaning (information, definition, explanation, facts)

The GNU Lesser General Public License (formerly the GNU Library General Public License) is an FSF approved Free 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 was written in 2000 by Richard Stallman and Eben Moglen.

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 primarily intended for software libraries, although it is also used by applications such as OpenOffice.org.

The main difference between the GPL and the LGPL is that the latter can be linked to a non-(L)GPLed program, which may be free software or proprietary.

One feature of the LGPL is that you can convert any LGPLed piece of software into a GPLed piece of software (section 3 of the license). This is useful if you want to create a version of the code that proprietary software companies cannot use in non-free software products.

The LGPL is now deprecated by the FSF, on the grounds that a GPLed library forces the software using it to be under the GPL also, and hence creates more free software.