A [directed acyclic graph](https://en.wikipedia.org/wiki/Directed_acyclic_graph) (DAG) is graph whose edges are given a direction ("a to b" is not the same edge as "b to a"), and for which no possible path (created by joining together edges) forms a cycle.

  DAGs are very important to Nix.
  In particular, the non-self-[references][reference] of [store object][store object] form a cycle.

- [derivation path]{#gloss-derivation-path}

  A [store path] which uniquely identifies a [store derivation].

  See [Referencing Store Derivations](@docroot@/store/derivation/index.md#derivation-path) for details.

  Not to be confused with [deriving path].


- [derivation expression]{#gloss-derivation-expression}

  A description of a [store derivation] using the [`derivation` primitive](./language/derivations.md) in the [Nix language].


- [instantiate]{#gloss-instantiate}, instantiation

  Translate a [derivation expression] into a [store derivation].

  See [`nix-instantiate`](./command-ref/nix-instantiate.md), which produces a store derivation from a Nix expression that evaluates to a derivation.


- [realise]{#gloss-realise}, realisation

  Ensure a [store path] is [valid][validity].

  This can be achieved by:
  - Fetching a pre-built [store object] from a [substituter]
  - [Building](@docroot@/store/building.md) the corresponding [store derivation]
  - Delegating to a [remote machine](@docroot@/command-ref/conf-file.md#conf-builders) and retrieving the outputs

  See [`nix-store --realise`](@docroot@/command-ref/nix-store/realise.md) for a detailed description of the algorithm.

  See also [`nix-build`](./command-ref/nix-build.md) and [`nix build`](./command-ref/new-cli/nix3-build.md) (experimental).


- [content-addressing derivation]{#gloss-content-addressing-derivation}

  A derivation which has the
  [`__contentAddressed`](./language/advanced-attributes.md#adv-attr-__contentAddressed)
  attribute set to `true`.

- [fixed-output derivation]{#gloss-fixed-output-derivation} (FOD)

  A [store derivation] where a cryptographic hash of the [output] is determined in advance using the [`outputHash`](./language/advanced-attributes.md#adv-attr-outputHash) attribute, and where the [`builder`](@docroot@/language/derivations.md#attr-builder) executable has access to the network.

- [store]{#gloss-store}

  A collection of [store objects][store object], with operations to manipulate that collection.
  See [Nix Store](./store/index.md) for details.

  There are many types of stores, see [Store Types](./store/types/index.md) for details.


- [Nix instance]{#gloss-nix-instance}
  <!-- ambiguous -->
  1. An installation of Nix, which includes the presence of a [store], and the Nix package manager which operates on that store.
     A local Nix installation and a [remote builder](@docroot@/advanced-topics/distributed-builds.md) are two examples of Nix instances.
  2. A running Nix process, such as the `nix` command.

- [binary cache]{#gloss-binary-cache}

  A *binary cache* is a Nix store which uses a different format: its
  metadata and signatures are kept in `.narinfo` files rather than in a
  [Nix database]. This different format simplifies serving store objects
  over the network, but cannot host builds. Examples of binary caches
  include S3 buckets and the [NixOS binary cache](https://cache.nixos.org).

- [store path]{#gloss-store-path}

  The location of a [store object] in the file system, i.e., an immediate child of the Nix store directory.

  > **Example**
  >
  > `/nix/store/a040m110amc4h71lds2jmr8qrkj2jhxd-git-2.38.1`

  See [Store Path](@docroot@/store/store-path.md) for details.


- [file system object]{#gloss-file-system-object}

  The Nix data model for representing simplified file system data.

  See [File System Object](@docroot@/store/file-system-object.md) for details.


- [store object]{#gloss-store-object}

  Part of the contents of a [store].

  A store object consists of a [file system object], [references][reference] to other store objects, and other metadata.