grunt-preprocess is a Grunt task that enables conditional preprocessing of files based on custom or environment-based variables. It's useful for creating different versions of your application for development, staging, or production environments from a single source. By defining directives within your files, grunt-preprocess selectively includes or excludes specific code blocks during the build process, streamlining the deployment of environment-specific configurations and features. This tool enhances code maintainability and simplifies deployment pipelines.