Open source is software that you can use for free
Open source refers to software that anyone can study, use, change and copy at their discretion. Twenty-five years ago, “free software” began as a small group of developers who rebelled against the commercialisation of their work. Nowadays, open source programs cover large areas of the internet and are in competition with major software companies.
Open source has thus become a kind of worldwide social movement which stands for making software, as well as knowledge and culture, available to everyone. From Open Access to Creative Commons, from Wikipedia to Edubuntu, thousands of people around the world are working on a collective wealth of free knowledge, discover new forms of cooperation and public spiritedness and contradict all the rules of copyright and the economy.
Open source is not a copyrighted trademarked term
The basic idea behind the open source movement in software is that the user has more rights to the software. This primarily means the right to freely distribute the program, the right to obtain the source code, to change the software and to pass it on to others in this form, and the right to use the software for any purpose.
After its establishment in 1998, the Open Source Initiative sought to protect open source as a trademark. However, this failed because the term “open source” was held to be too generic to gain trademark protection. From a purely legal point of view, anyone can therefore define the open source however they want.
This then leads to the problem of what is viewed as open source and what is not. In the meantime, users have built up a broad consensus on what is open source. Whoever uses open source programs can expect that the manufacturer grants certain rights – rights that the Open Source Initiative sets in its definition, how it promotes the Free Software Foundation and how it grants the well-known Open Source licenses like Apache or Mozilla Public License.
You can find more information on Open Source on Wikipedia: https://en.wikipedia.org/wiki/Open-source_model
There is also an article on Wikipedia on the Open Source Initiative: https://en.wikipedia.org/wiki/Open_Source_Initiative