Open source 101

Open source software is software provided on terms allowing user to use, modify, and distribute the source code. It is different from freeware or shareware. In the open source world, "free" usually means "freedom to modify and redistribute source code" rights that do not necessarily come with freeware or shareware.

An open-source license is a copyright license for computer software that makes the source code available for everyone to use. Copyleft licenses require that you share any modifications that you make to the original code. Usually, these licenses also require that you share these modifications under the exact same open source software license as the source code. Different open source licenses have different levels of copyleft, namely No Copyleft, Weak Copyleft and Strong Copyleft.

Here are a list of common licenses:

• GPL v.3 - GNU General Public License, version 3   
• LGPL v.3 - GNU Lesser General Public License, version 3 (sometimes referred to as the "Library" General Public License)   
• GPL v.2 - GNU General Public License, version 2   
• LGPL v.2.1 - GNU Lesser General Public License, version 2.1 (sometimes referred to as the "Library" General Public License)   
• MPL - Mozilla Public License, version 1.1   
• Eclipse - Eclipse Public License, version 1.0   
• CPL - Common Public License, version 1.0   
• CDDL - Common Development and Distribution License, version 1.0   
• MIT - MIT License   
• BSD - Berkeley Software Distribution License or "New BSD"

Take away:
Feel free to use MIT/BSD license which has no copyleft, try to avoid GPL which has strong copyleft. MPL, Eclipse, CPL, CDDL are falling into weak copyleft category.