Open source is software's source code that is freely available to everyone. Drupal, Wordpress, Linux are examples of open source software.
Anyone can study, edit, and distribute the software for any purpose, as specified in the Open Source Initiative : http://opensource.org/docs/definition.html.
It has never been easier to build your own website, with online services that offer free website templates, simply add your text and picures. If more control is required there are options such as Wordpress, Joomla and Drupal. There are many sites built with Wordpress, arguably the easiest of the open source web building applications, with fast installing available on most cpanel shared hosting. Drupal is a powerful open source option that is extremely flexible and accomplishes almost any web site task.
Hairy Camel Web solutions uses Drupal for most web site applications, and Magento for e-commerce sites.