It is a design pattern, one that predates both Java and the GoF book. It's a Smalltalk idiom. I think Kent Beck was the first to describe it in one of his books, "Smalltalk Design Patterns".
Design patterns are proven solutions to object-oriented programming problems. The GoF book was valuable because it put some structure around the way patterns were written up, but it's not the sole source.
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Here is a link about MVC as a design pattern
http://www.enode.com/x/markup/tutorial/mvc.html
It begins: "
Model-View-Controller (MVC) is a classic design pattern often used by applications that need the ability to maintain multiple views of the same data. The MVC pattern hinges on a clean separation of objects into one of three categories ?models for maintaining data, views for displaying all or a portion of the data, and controllers for handling events that affect the model or view(s).
Because of this separation, multiple views and controllers can interface with the same model. Even new types of views and controllers that never existed before can interface with a model without forcing a change in the model design."