Unix
In plain terms
A foundational operating system that influenced modern OSes.
Going deeper
Unix introduced enduring concepts, files, processes, pipes, and a modular philosophy, that shaped Linux, macOS, and others. Its ideas are everywhere.
Under the hood
The Unix philosophy (small tools, do one thing well) and POSIX standard persist across descendants.
Examples
Unix philosophy, POSIX, macOS/BSD roots, command-line tools, pipes.
Think of it like...
Like the ancestral design that nearly all modern operating systems descend from.