Too late to edit, but here's the inarguable truth straight from the mouth of the Open Source Initiative, that the term was the direct product of Netscape's desire to get people to work for them for free: https://opensource.org/history

“The ‘open source’ label was created at a strategy session held on February 3rd, 1998 in Palo Alto, California, shortly after the announcement of the release of the Netscape source code. […] The conferees believed the pragmatic, business-case grounds that had motivated Netscape to release their code illustrated a valuable way to engage with potential software users and developers, and convince them to create and improve source code by participating in an engaged community. The conferees also believed that it would be useful to have a single label that identified this approach and distinguished it from the philosophically- and politically-focused label ‘free software.’”