For the sake of argument, let's define a miracle to be something fantastically improbable.
Suppose that we have a biased coin that, if flipped, would almost always land tails-side up with a mathematical probability of (1-p); otherwise, it would land heads-side up with a mathematical probability of p.
By the threshold of intolerable improbability, I mean the largest mathematical probability p such that if we flipped our biased coin just once and it lands heads-side up, then there's nothing miraculous about that at all, but if we flipped that coin a second time and it lands heads-side up for a second time in a row, then we know that we have violated a known law of physics
It seems to me that you are substituting the word "miracle" for the phrase "something fantastically improbable". You could have used any word or even a symbol. So all we have to do is substitute back into your sentence the phrase or (similar depending on the grammar), in order to remove any connotations associated with the word. Thus we obtain...
"Suppose that we have a biased coin that, if flipped, would almost always land tails-side up with a mathematical probability of (1-p); otherwise, it would land heads-side up with a mathematical probability of p. By the threshold of intolerable improbability, I mean the largest* mathematical probability p such that if we flipped our biased coin just once and it lands heads-side up, then there's nothing fantastically improbable about that at all, but if we flipped that coin a second time and it lands heads-side up for a second time in a row, then we know that we have violated a known law of physics ".
Now we don't need the definition and all is clear, except, perhaps you mean smallest here * and I'm not sure which law of physics you mean.
I assume p is a very small number, say 1/1000 which makes (1-p) = 999/1000
So your biased coin lands tails-side up 999 times in 1000, and heads up 1 time in a 1000.
Suppose you get a head followed by another head, the likelihood of two heads in a row is the product of the individual probabilities, i.e. 1/1000 x 1/1000 = 1/1000000
which is, one has to agree, a much smaller number than 1/1000 and in therefore the outcome is very rare, but not impossible.
However, if a billion pairs of biased coins were flipped, a pair of heads would be quite likely and nobody would consider that event a violation of a law of physics.
Similarly, if you won the lottery, it wouldn't be a violation of any law, it would be just be an unlikely, but hopefully, welcome event.
Suppose you didn't buy a ticket, but won the lottery anyway. Would you call that a miracle or a mistake ?
Many years ago, I received a pay packet from my employer, that included an extra amount called "back pay".
I wasn't expecting it and was very pleased. It almost doubled my pay for that week.
A week or so later, a wages clerk phoned me and apologized for the error.
The payment was supposed to go to another employee who had recently been promoted.
I was asked to agree to a pay cut the following week to correct the error. I was not so pleased.
This was a unique event in my life, but I wouldn't call it a miracle.