"What defines upstream? KDE, GNOME, Apache, even the Linux
kernel are upstream for a Linux distribution, and even a totally
different distribution altogether may be considered upstream (for
example, Debian is considered upstream for Ubuntu). These upstream
projects are the ones that write most of the code that goes into
powering your free software operating systems, and to a
distribution, they are what makes the whole thing possible. There
is a fine but delicate process that happens to keep all of these
projects all running as smoothly as they do. Distros have been
known to fail due to making too many changes to the source without
the cooperation of their upstream partners.
"You can trace the path even further upstream: KDE, which is
already upstream for a distribution, depends on code that comes out
of a wide variety of library projects, such as the popular Qt
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