What is Software Design Pattern?

Patterns originated as an architectural concept by Christopher Alexander (1977/79). In 1987, Kent Beck and Ward Cunningham began experimenting with the idea of applying patterns to programming and presented their results at the OOPSLA conference that year. In the following years, Beck, Cunningham and others followed up on this work.

Design patterns gained popularity in computer science after the book Design Patterns: Elements of Reusable Object-Oriented Software was published in 1994 by the so-called "Gang of Four" (Gamma et al.), which is frequently abbreviated as "GoF". That same year, the first Pattern Languages of Programming Conference was held and the following year, the Portland Pattern Repository was set up for documentation of design patterns.

For more info, visit the links below:
http://en.wikipedia.org/wiki/Software_design_pattern
http://en.wikipedia.org/wiki/Design_Patterns
http://en.wikipedia.org/wiki/Gang_of_Four_(disambiguation)