Deferred Static Generation (DSG), introduced in Gatsby 4, is a rendering technique that defers the building of certain web pages until they are requested at run-time, allowing them to be built on the fly during the first user request. This method enables developers to mark pages as deferred during the initial build, omitting them from static site generation, and only rendering them when a user accesses them, after which they behave like any other static page. DSG ensures atomic builds by utilizing snapshotted data from build time, maintaining site integrity across both static and deferred pages. Unlike Incremental Static Regeneration (ISR) developed by Next, which updates pages across multiple builds and can lead to inconsistent data display, DSG is less brittle as it relies on cached data rather than server-side API calls. Developers can strategically choose which pages to defer, such as older blog posts, less popular eCommerce products, or past versions of documentation, optimizing the balance between developer and user experience. Implementing DSG involves using the defer argument in the createPages action, deciding whether to exclude certain pages from the build step to enhance efficiency and manage performance impacts.