My problem is that even if I knew the precise definition of what they mean by "ether" it wouldn't help me, because in the end I have no idea what the heck that mysterious "stuff" could be. Another words -- there's insufficient data to arrive at a logical conclusion.
To complicate things, there are several proposed kinds of 'ether' and 'ether' means many different things to different authors and scientists.
The type of 'ether' that Einstein originally rejected and successfully proved (by relativity) doesn't exist was the type that was logically inconsistent with relativity. But then he later decided that another type of 'ether' that is NOT inconsistent with relativity may (or even does) exist.
That means, contrary to what stupid metalbrain claims he made in some past posts, he was never wrong about rejecting the existence of ether because the kind of 'ether' he originally rejected is proven to not exist by relativity and the 'ether' he later talked about wasn't that type of ether but a different kind of proposed ether that does NOT contradict relativity thus, contrary to what stupid metalbrain claims, ether did NOT prove Einstein wrong about relativity. Relativity has NEVER been proven simply wrong and relativity is at least in the main correct.
I don't know why but I have noticed that the internet is full of posts from many ignorant delusionally arrogant laypeople that are an extremely loud minority (or at least I really hope they are just a minority) who think they can prove relativity and Einstein wrong because they think they are smarter than the likes of Einstein. They all give different said 'reasons' or 'arguments' for relativity and Einstein being wrong and all of those so-called 'reasons' and 'arguments' I have read, without a SINGLE exception, are all just complete BS and show almost all of them don't understand the first thing about relativity even though they make out they understand everything about relativity while apparently none of them being able to even handle any of even the simplest equations of relativity. Some have even called Einstein "stupid" or "an idiot"; Such are their ignorant arrogant delusions.