This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
"Multidimensional" means that data can be indexed by as many parameters as needed - it is not constrained to fit into rows and columns. This allows for much richer data models than can be achieved using relational technology. Complex data can be stored and used in a much more natural way.