# System specificity

In Nix, the term _system specificity_ expresses the fact that all Nix [derivations] have a `system` attribute that specifies which system the derivation is built on.
In order to realize a Nix derivation into a [package], each derivation in the package's closure needs to be supported on the target system.
So if you want to build the package `foo` on an `x86_64-linux` system, any dependency of the `foo` derivation needs to be supported on `x86_64-linux`.

System specificity is essential to Nix being a truly multi-platform system.
Because all derivations—and thus all packages—are system specific, things like Nix [development environments][env] and [NixOS] configurations are also system specific.

[derivations]: /concepts/derivations
[env]: /concepts/dev-env
[nixos]: /concepts/nixos
[package]: /concepts/packages