OS OS is an abbreviation for Operating System, which is software that manages the entire system. Windows and Mac, which everyone uses as PCs, are also OSs.
Linux An OS called Linux is often used for programming. Unlike Windows and Mac, Linux strictly refers to the core part of the OS (Linux kernel).
In order to operate as a practical OS, it is necessary to combine software that handles various functions such as screen display, communication, and file management in addition to the kernel. If you compare it to a car, the kernel is the engine. The engine is the core of the car, but parts such as brakes, accelerators, and steering wheels are required for the car to run.
Combining the Linux kernel and software to create an operating system that actually works requires in-depth knowledge of the Linux kernel itself and the operating system, which is not realistic.
Therefore, there are some that are distributed in a nice combination of Linux kernel and various software so that general users and developers can easily use Linux. This is the "Linux distribution". In general, various Linux distributions are often collectively referred to as "Linux".
There are various Linux distributions that are optimized for various purposes, such as those that emphasize stability for servers and those that can be used comfortably on older PCs.
The reason for using Linux for programming is that Linux has a wealth of programming software and is convenient. In addition, Linux is licensed under the GNU General Public License (GPL), so it's basically free to use. This has the advantage of significantly reducing costs in server operations, which require a huge number of PCs. Therefore, Linux is widely used in the world of Web programming.