This script, `_ssgManifest.js`, is a core component of Next.js applications that utilize Static Site Generation (SSG). It acts as a manifest file, containing metadata about the statically generated pages and their associated data. When a user navigates between pages on an SSG Next.js application, this manifest helps the client-side JavaScript efficiently determine which data to fetch or which pre-rendered content is available, without requiring a full page reload from the server. It is crucial for client-side routing and prefetching capabilities, ensuring a smooth and fast user experience by leveraging the benefits of static rendering with dynamic client-side interactions.