People say mastodon is too hard to explain to non-technical people, but I explained it the other day to someone extremely non-technical by just saying "it's decentralised. so instead of being run by one company, it's run by whoever wants to run their own version of it. This way there's no profit incentive, no algorithm and no ads" and she immediately understood what I meant, and why that would be a good thing.
You don't really need to explain federation and all the underlying tech to explain people what it is. Even federation is simple to explain. "anyone can run their own version of it - but they can all still talk to each other"