A design pattern is a general reusable solution to a

commonly occurring problem in software design. A design

pattern is not a finished design that can be transformed

directly into code. It is a description or template for how

to solve a problem that can be used in many different

situations. Object-oriented design patterns typically show

relationships and interactions between classes or objects,

without specifying the final application classes or objects

that are involved.

Design patterns reside in the domain of modules and

interconnections. At a higher level there are Architectural

patterns that are larger in scope, usually describing an

overall pattern followed by an entire system.