Organically related to the annotation regarding my nix-shell confusion.
The dissection of this definition to show why I find it lacking:
A description of a build action.
The first (couple) time(s) I read the manuals, this description popped up in many places, and I identified it with Nix expression every time, thinking that a derivation is a synonym for Nix expression.
Maybe it is, because it clearly tries to disambiguate between store derivations and derivation in the last sentence.
The result of a derivation is a store object.
Is this store object the same as a store derivation?
Derivations are typically specified in Nix expressions using the `derivation primitive. These are translated into low-level store derivations (implicitly by nix-env and nix-build, or explicitly by nix-instantiate).
QUESTION: So, the part of the Nix build expression (such as default.nix) where the derivation primitive is called (explicitly or implicitly, as in mkDerivation) is the derivation, that will be ultimately be translated into store derivations?
ANSWER: Start at section 15.4 Derivation.
QUESTION: Also, why is typically used here? Can one define derivations outside of Nix expressions?
ANSWER(?): One could I guess, because store derivations are ATerms (see annotation at the top), and the Nix expression language is just a tool to translate parameterized build actions into concrete terms to build a software package. The store derivations could be achieved using different means; e.g., the way Guix uses Guile scheme to get the same result))
I believe, that originally, derivation was simply a synonym to store derivation. Maybe it still is, and I'm just having difficulties with reading comprehension but I think the following would be less misleading (to me and apart from re-writing the very first sentence):
Derivations are typically the result of Nix expressions calling the derivation primitive explicitly, or implicitly usingmkDerivation`. These are translated into low-level store derivations (implicitly by nix-env and nix-build, or explicitly by nix-instantiate).