Check and change Raspbian package sources
Simply Linux is a kernel and packages. Packages include programs, libraries and drivers. Packages can build on each other and often depend on other packages. The versions of the packages and their dependencies are managed in the package sources. The repositories provide lists of the packages and their dependencies.

Each Linux distribution may have different and multiple repositories (repository, software archive).
Occasionally there are reasons to change or supplement the sources of the packages.
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