Open source it's philosophy, methodology and culture movement, which declares free access to the source of the product. It's mean, what everybody could know how something works.
You could meet open source everywhere : computer science, robotics industry, medecine, beverages.
People shares what they like.
I'm a open source Web developer, so I share the code I make, participating into open source Web projects, as TYPO3, Drupal, and many others.
The open source license, I prefer, it's GNU General Public License, it's mean, what proposed open source code couldn't be sold inside any other commercial product.