Drupal is an Open Source Content Management System. If you are new to both computing and Drupal, then this probably doesn't clear things up very much. First of all:
The term open source describes software whose source code is made available, most often subject to certain conditions, for use or modification by users or other developers, as they deem fit.
The specific conditions under which Drupal is made available will be scrutinized more closely in the section The Drupal license later in this chapter.
Besides that, what open source means for someone who intends to make use of Drupal is that there is no obligatory payment required for this unquestionably valuable software. You also join a large community (also to be discussed ...