FOSS means Free and Open Source Software.
It doesn’t mean software is free of cost. It means that source code of the software is open for all and anyone is free to use, study and modify the code. This principle allows other people to contribute to the development and improvement of a software like a community.
The distinction is important because FOSS is a generic world and it could mean different depending on the context. Here, We are discussing the FOSS principle in software.
In the 60s and 70s, computers were hardware focused and the hardware were expensive. They were mainly used by academics in universities or researchers in labs. The limited amount of software used to come for free or with their source code and the users were allowed to modify the source code to suit their need.
In the late 70s and early 80s, the manufacturer’s stopped distributing source code in an attempt to not let their software run on their competitor’s computers.
This restrictive licensing led to the inconvenience and dislike of peoplewho were used to and fond of modifying software. In the mid 80s, Richard Stallman started the Free Software Movement.
Stallman specified four essential fundamental freedom for a software to be Free and Open Source Software.