Chapter 8. Coding and Design Patterns
But first, what's pattern? In short, a pattern is a good solution to a common problem.
Sometimes when you're facing a new programming problem, you may recognize right away that you've previously solved another, suspiciously similar problem. In such cases, it's worth isolating this class of problems and searching for a common solution. A pattern is a proven and reusable solution (or an approach to a solution) to a class of problems.