Open source means the source code of a piece of software is published for anyone to read, use, change and share, usually for free. The opposite is closed or proprietary software, where the code is hidden and you only get the finished product. With open source you get the recipe, not just the dish, so you can see how it works and adapt it to your needs.
A good analogy is a community cookbook. Anyone can follow a recipe, tweak it to their taste, and publish an improved version for the next cook. Over time the best ideas spread and the recipes get better. Software like Linux, Node.js and most of the libraries on npm work the same way, which is why a small team can build on decades of shared work instead of starting from zero. Many a framework that powers modern websites is open source too.
It is not a free-for-all, though. Every project has a licence that sets the rules, and they differ a lot. MIT and Apache 2.0 let you do almost anything, while GPL requires you to share your own changes back if you distribute the result. Ignoring those terms can cause real legal trouble. There is also a quieter risk: an open project can be abandoned by its maintainers, so checking when it was last updated and how many people contribute matters as much as reading the licence.
The other side of that openness is influence. Because the code is public, you can report a bug, propose a fix, or fund the maintainers, instead of waiting on a vendor’s roadmap.
At TopDevs we build on trusted open-source tools wherever it makes sense, and we keep a clear record of every licence in a client project so there are no surprises down the line.
