I was introduced to open source, as a concept, when working with some very talented developers years ago. They all had “free software” (that’s what open source was called at the time)—simple utilities that they gave away for free, code and all.
The term “open source” replaced free software after a time, really to rebrand this concept to reflect a more commercially minded group that looked for the commercial possibilities in this emerging movement. This gave birth to Linux, MySQL, MongoDB, Puppet, etc. (all still widely used today) and the rise of enterprises that prefer, or at least use, open source software.