Title: Theory / Unimportant / CS / command line / admin / apt / configuration
On every note of this deck, unless a note says otherwise:
Page: https://en.wikipedia.org/wiki/APT_(software)

Variable: /etc/apt/sources.list(.d/)
Meaning: Locations to fetch packages from.

Variable: /etc/apt/apt.conf(.d/)
Meaning: APT configuration file.

Variable: /etc/apt/preferences.d/
Meaning: Directory with version preferences files. This is where you would specify "pinning", i.e. a preference to get certain packages from a separate source or from a different version of a distribution.

Variable: /var/cache/apt/archives/
Meaning: Storage area for retrieved package files.

Variable: /var/cache/apt/archives/partial/
Meaning: Storage area for package files in transit.

Variable: /var/lib/apt/lists/
Meaning: Storage area for state information for each package resource specified in sources.list
Context: apt

Variable: /var/lib/apt/lists/partial
Meaning: Storage area for state information in transit.