Domain Modeling, Domain Objects in DDD

I'm really new to DDD and trying to grasp some of the concepts.

Could someone explain me the idea behind Domain Modeling in DDD.

I have already gone through wikipedia explanation: http://en.wikipedia.org/wiki/Domain_model but still seems like there are some gray areas in my understanding.

Based on what I understood, domain modeling involves building a model around the business entities to express their relationships, express the entities that participate in the model etc..

Isn't this something that has been in practice always? in Object Oriented world, you model business entities into classes, objects etc.. and build the software around this.

What I do not understand is the emphasis Domain Modeling gets in DDD. Is it the same object/class modeling that you find in OO world, or is this something new to DDD ? How does it differ from Object Oriented design/modeling?

Your answers are highly appreciated.