The Builder Pattern is defined in Design Patterns, Creational catagory. From Design Patterns:

Seperate the construction of a complex object from its representation so the the same constrution process can create different representations.

This pattern consists of a Builder class, which defines one or more methods to create objects. Typically, the Builder can construct different representations of the same data.

For example, a document converter object could take an internal representation of a document, and convert it to multiple formats, such a text, HTML, or a Microsoft Word document.

This pattern allows the code for construction to be isolated from the representation. It is appropriate for classes that have very complex construction requirements.