A monorepo is a repository that contains multiple sites or apps, each in its own subdirectory, allowing for easier tracking and management of common elements across projects. With the latest Netlify update, working with monorepos has become significantly easier, enabling automatic deployment and cancellation of builds based on changes detected in the base directory. The new `build.ignore` config option also simplifies splitting a monorepo into multiple Netlify sites, making it more efficient to manage and deploy multiple sites from one repository.