Design Pattern

hi,

Design patterns are recurring solutions to software design problems we face it again and again in real-world application development.
Design Patterns are how we design and interaction with objects, as well as providing a communication between two methods or functions (simply call element), reusable solutions to commonly encountered programming challenges.

 All are depend on our requirement and how I design architecture.

In real world, all code is from of pattern example suppose I want retrieve data from cache so I write common mechanism to retrieve data from cache. It is one type of pattern we can call them repository pattern.

This is just example.

hope this help.

There are numerous of patterns in the market. Even if you can find some thing new which other they do not discovered then it became pattern. 

        You can see more patterns in  http://www.dofactory.com/Patterns/Patterns.aspx 
 
The usage of the pattern is upto the implementation of system.For example you have a system where it will keep on listening the request and same object has to be reused to increase the performance of the application. It should not create more number of object to accessing the same resources then "Singleton" pattern has to be used.