Open-source is code, that is made available publicly. Often, also allowing for modification and further distribution.
Open source vs. proprietary software
Open source is often considered the opposite of proprietary software. It must be denoted, however, that open source software can still enable its developer to make financial profits. A common model is developing open source software and allowing others to use it freely, but offering paid services, such as support and consulting on top.
”Indirectly open source”
The frontend in web apps is indirectly open source, as you can view the source code in the browser’s DevTools.
Closed source
Software, which doesn’t share its code publicly.
Typical cases of closed-source applications mobile apps you can download and other prio