Design patterns present solutions to reocurring design issues in object oriented design. Note that this is not presented as finished code, but as a design that presents a solution to be implemented for a pattern of similar problems.
The basic of design patterns is the use of templates that is a well-known, tested and generalized solution to a certain problem. Likewise, it delivers known names for many of the solutions, supposedly easing communication among developers.
The idea became popular whith the 1994 book Design Patterns: Elements of Reuseable Object-Oriented Software. The authors, Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides, is usually known as the Gang of Four or just GoF.