Jenkins is an open-source automation tool that supports Continuous Integration/Continuous Deployment (CI/CD) and provides a flexible way to configure builds, automate workflows, and streamline deployment processes through environment variables. Environment variables in Jenkins are key-value pairs that store configuration settings, credentials, and other dynamic values used during build and deployment processes, helping to make pipelines more flexible by allowing scripts and jobs to reference variables instead of hardcoded values. Built-in environment variables provide essential context about pipeline configurations, eliminating the need for hardcoding specific script values and making pipelines more adaptable. Jenkins offers global and local environment variable management options, including a Credentials Plugin that securely stores sensitive information such as usernames, passwords, and credentials. The tool also provides various plugins to enhance credential management, infrastructure orchestration, and automation workflows.