A shared module exports providers so other modules can import it explicitly. A global module (decorated with @Global()) registers its exported providers application-wide so no explicit import is needed. Global modules should be registered only once in the root module and used sparingly to avoid hidden coupling.
A shared module is the standard pattern — it exports providers and must be imported explicitly by any module that wants to use them. A global module uses @Global() so its exports are available everywhere without needing to be imported.
Shared module — default choice; explicit imports keep dependencies traceable.
Global module — use only for truly cross-cutting infrastructure like logging, config, or database connections.
Global modules should be registered only once, in the root AppModule.
Overusing @Global() leads to hidden coupling and makes modules harder to test in isolation.