When we talk about "free software," we're not talking about software that doesn't cost anything (although that's often true too!). Instead, we mean software that is "free" in the sense that you have certain freedoms when you use it.
These freedoms include the freedom to use the software for any purpose, to study how it works (if you're curious or if you want to make changes), to distribute copies of the software to others, and to improve the software and distribute those improvements to others. Essentially, "free software" means that the users have control over the software they use instead of being controlled by the company or individuals who created it.
Now, the term "free software" might be a little confusing, because "free" can mean either "no cost" or "freedom." Therefore, some people and organizations opt to use different terms such as "open source" software, which means roughly the same thing as "free software" but emphasizes the ability of users to access the source code and modify it.
Other alternative terms for "free software" include "libre software," which comes from the Spanish word for "free" and stresses the idea of freedom, and "FOSS" or "FLOSS," which stand respectively for "Free and Open Source Software" and "Free/Libre and Open Source Software."
All of these terms ultimately refer to software that is designed to give users more control over their computing experience, and to encourage collaboration and innovation between users and developers.