Free and open source software, often shortened to FOSS, is software whose source code is published openly so that anyone can read it, use it, modify it, and share it. The "free" here refers to freedom, not just price, although most FOSS is also free to download. The core idea is that the inner workings are not locked away. Anyone can inspect exactly how the software behaves and build on top of it.
A helpful comparison is a published recipe versus a secret one. Proprietary software is like a dish made from a recipe the restaurant will never reveal. You can buy the meal, but you cannot see how it was made or change the ingredients. FOSS is like a recipe printed in full. You can cook it yourself, adjust it to your taste, and pass your version along to others. Linux, the operating system that runs most of the internet, is a famous example, as are tools like Firefox and countless programming libraries.
For businesses, FOSS matters for three reasons: cost, transparency, and control. There are no license fees, you can verify what the software actually does rather than trusting a vendor's word, and you are not locked into one supplier. The trade-off is that you take on more responsibility for support, security updates, and making sure the pieces you assemble actually work together reliably.
Usually yes, but that is not the main point. "Free" refers to the freedom to use, study, change, and redistribute the software. Some FOSS projects sell paid support or hosted versions on top of the free code, which is a common business model.
It can be very safe, and in some ways safer than closed software, because anyone can inspect the code for flaws. Widely used FOSS like Linux is reviewed by thousands of people. The risk comes from small, unmaintained projects, so the key is choosing well-supported, actively maintained software.
A free trial or freemium product is still closed software owned by one company that controls it. FOSS gives you the actual source code and the legal right to modify and share it. You are not just borrowing access, you have genuine ownership of how it runs.
Yes, that is one of its main benefits. If a tool almost fits your process but is missing something, you or a developer can change the code directly. With proprietary software you would have to wait for the vendor to add the feature, if they ever do.
The main one is responsibility. With FOSS, support is often community-based rather than guaranteed, and you must keep components updated yourself. There are also licenses to respect, since "open" does not mean "no rules." Some licenses require you to share changes you make.
Much of modern AI is built on open source foundations, including many models, libraries, and frameworks. This lets companies build on shared, transparent technology rather than starting from scratch, and it makes it easier to understand and audit how a system works.