Spack environments are a powerful feature of the Spack package manager that enable users to create isolated and reproducible environments for their software projects. Each Spack environment contains a specific set of packages and dependencies, which are installed in a self-contained directory tree. This means that different projects can have different versions of the same package, without interfering with each other. Spack environments also allow users to share their software environments with others, making it easier to collaborate on scientific projects.