S.O.L.I.D principles

S: The Single Responsibility Principle
O: The Open Closed Principle
L: The Liskov Substitution Principle
I: Interface Segregation Principle
D: The Dependency Inversion Principle

Five principles that made the OOP world is re-use and easily maintain.
All thing is found by Robert Martin (a.k.a. Uncle Bob). And today, i find a link that write very good about S.O.L.I.D principles. You can find this at here.