# What is Hydra?

Hydra is, more or less, a build server. Unsurprisingly, it uses [Nix and nixlang](https://wiki.slightly.tech/books/learning-nixos/page/what-is-nix "What is Nix?") for specifying what to build. It's used to build the binary packages for [nixpkgs](https://wiki.slightly.tech/books/learning-nixos/page/what-is-nixpkgs "What is nixpkgs?"), for example, as well as for running automated tests to ensure that packages actually work. If you're just using Nix or [NixOS](https://wiki.slightly.tech/books/learning-nixos/page/what-is-nixos "What is NixOS?") as an end user, you probably don't need to care about this.

Because Hydra supports deployment operations after a successful build-and-testing cycle, you could also technically consider it a Continuous Deployment system.