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.

At work, I have a very knowledgeable colleague who is quite the Linux nerd. I have been moved into their department and I feel like they never had the chance to share all of their accumulated knowledge with someone, so they kinda dump it onto me and every little question has the chance to become a lecture. I am very thankful for it though, because I get learn a ton but sometimes you just wanna get a bool, without learning kernel internals that are absolutely not related to the question