This is the classical understanding of it. Determinism basically says "given some initial state of the universe, you can pre-determine the end state before it happened". E.g. there would be enough information at any point in the timeline of the universe before the 9/11 terrorist attack to infer that it will happen, just like with your coin flip example. So the question becomes whether true randomness exists. If it does, then it will have a major say in how the universe evolves between its beginning and 9/11, due to how chaotic systems work. Your coin flip example is a typical argument against true randomness, but modern quantum mechanics challenge this point of view, opening up some more interpretations. I suggest the Wikipedia article on Determinism. It has some very interesting points.