SOLID is an acronym that represents five design principles in object-oriented programming aimed at making software designs more understandable, flexible, and maintainable. The principles are: Single Responsibility Principle, Open/Closed Principle, Liskov Substitution Principle, Interface Segregation Principle, and Dependency Inversion Principle. Together, they help developers create systems that are easier to manage and extend over time. By following SOLID principles, developers can reduce the risk of bugs and improve code readability. Each principle addresses a specific aspect of software design, encouraging practices like keeping classes focused on a single task and ensuring that modules can be easily replaced or modified without affecting the entire system.