Licenses: Commercial, Proprietary, Non-Open source & Open Source
OSS have Open Source License:
Allows: Modification & Redistribution
Disallows: Discriminatory or over restrictive access to source code
Copyright: A set of legal protections granted by law
License: How copyright holder grants permissions to licensee/party
Open source operates under/within licensing covered by copyright law


OPEN SOURCE LICENSES:
- Applied to source code as well as compiled binary code
- Commercial licenses don’t override open source licenses. All licenses are important as per requirement
Types of Open Source Licenses:
- Copyleft License: Requires distribution of source code. Difficult compliance & extensive obligations
- Weak Copyleft - LGPL, Mozilla, Eclipse, CPL
- Strong Copyleft - GPLv2/v3 , AGPL
- Extreme Copyleft - SSPL, NPSL
- Attribution Style License: Requires distribution of copyright & license. Easy compliance & Simple obligations.
- No Copyleft - BSD, MIT, Apache
GPL - GNU General Public License (Original Type of Copyleft License)
- GPL - 1989
- GPLv2 - 1991 - Individual Open Source, Use in Linux Kernel, Most famous currently
- GPLv3 - 2007 - Made to address new issues, limited adoption currently, More complex
ISSUES:
- Contamination of Source Code -
- Merges GPL with non-GPL code & Imposes GPL Terms on other software
- Method of interaction either by static linking i.e. direct sharing. Set of routines, external functions & variables that are resolved in a caller at compile time (high risk)
- or by dynamic linking like sharing memory spaces. Subroutines of a library are loaded into application program at runtime (moderate risk)