What does the term "dependency injection" refer to in software design?

The term "dependency injection" refers to a technique where a class receives dependencies from external sources rather than creating them internally. This approach promotes a clean separation of concerns, making code more modular, testable, and maintainable. By relying on external sources for the creation of dependencies, classes can be better decoupled from specific implementations. This allows for easier swapping of implementations, which is particularly beneficial when testing or modifying code, as dependencies can be easily mocked or replaced.

In practice, dependency injection can be implemented through various methods, such as constructor injection, setter injection, or interface injection, providing flexibility in how dependencies are provided to a class. This pattern enables better management of object lifetimes and scopes, improving the overall design of a software system.