The word SOLID acronym for:

• Single Responsibility Principle (SRP)

  each class must perfom single functionality

• Open-Closed Principle (OCP)

  the module should be open for extension but closed for modification.

• Liskov Substitution Principle (LSP)

  derived classes must be completely substitutable for their base classes.

• Interface Segregation Principle (ISP)

  the larger interfaces split into smaller ones. Because the implementation classes use only the methods that are required

• Dependency Inversion Principle (DIP)

  use abstraction (abstract classes and interfaces) instead of concrete implementations.

  High-level modules should not depend on the low-level module but both should depend on the abstraction.

Further Reading: