Discuss 'Module Augmentation' vs 'Global Augmentation'.

Module augmentation extends a specific third-party module, while global augmentation extends the global namespace (like Window).

TypeScript's declaration merging allows you to add members to existing interfaces. Module augmentation is used when you want to add a method to a library like 'Express' or 'Knex'. You wrap the interface in a declare module 'library-name' block. Global augmentation is used for browser-wide or process-wide objects like process.env or Document. This is essential for maintaining type safety when using middlewares or polyfills that modify external objects.