What does the letter D stand for in the SOLID principles of programming?

The letter D in the SOLID principles stands for the Dependency Inversion Principle.

The essence of this principle is that:

• High-level modules should not depend on low-level modules. Both should depend on abstractions.
• Abstractions should not depend on details. Details should depend on abstractions.

This helps reduce code coupling and increase its flexibility and testability. For example, instead of a class directly creating instances of dependencies, it receives them through interfaces or abstract classes.