Lerna is a tool used in software development that helps manage projects with multiple packages. It simplifies the process of working with JavaScript projects that are divided into smaller, reusable components. By using Lerna, developers can easily share code, manage dependencies, and streamline the workflow of their projects. One of the key features of Lerna is its ability to link local packages together, allowing for efficient testing and development. It also supports versioning and publishing of packages, making it easier for teams to collaborate. Lerna is commonly used in conjunction with other tools like npm and Yarn to enhance the development experience.