Linux is an operating system, that is, a set of essential programs to make the computer work and do something useful or fun. It is an alternative to Windows and MacOS, and can be installed in their place (or together, on the same computer).
More generally Linux is the first representative of the so-called "free" software ("freesoftware", in English), that software that is distributed with a license that allows not only the use by anyone and under any circumstances but also editing, copying and analysis.
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