In software engineering, 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.Not all software patterns are design patterns. For instance, algorithms solve computational problems rather than software design problems.credits : http://en.wikipedia.org/wiki/Design_pattern_(computer_science)