From LXF Wiki
A term often associated with Linux software and users. Usually refers to groups/software being free for use. Some software, like OpenVMS, isn't open source but the 'open' refers to standard support (POSIX, X etc).
OpenGL - A free widely available graphics language.
URL  (http://www.opengl.org/)
Open Source - The open source initiative. Source being the programming language code used to write software.
URL  (http://www.opensource.org/)