What is a miracle? The question has plenty of implications. Let's talk it through. The definition, typically, is something supernatural (performed by God). But, what is supernatural?
Literally, supernatural is "outside of nature". What makes that hard is the assumed knowledge of natural limits. To say supernatural, we imply impossibility (regardless of probability).
Consider centuries past, inadvertent exposure to antiviral agents healed the sick - miraculously. Their ignorance saw a supernatural explanation. Yet, we explain it naturally, exorcising the "miracle".
It's "God of the gaps" all over again - explaining the unexplainable with God until we discover the science and erase God. Can God only be part of things we can't explain?
Two paragraphs ago, I mentioned probability. Now, I believe that although miracles can be supernatural, they can also be improbable natural occurrences. Let me give you an example:
Pretend you have a virus. A man, whose autoimmune system saved him, mistakenly oozes his anti viruses into your open wound. You are saved. Is it supernatural? No. Is it a miracle? Why not.
I like to think miracles are events with God as choreographer. He doesn't care about natural or possible; He doesn't care about probabilities; He just does what He wants to His own end. See?
It's another topic of "how" God can enact His supernatural will on natural matter. Obviously He can. But still, it's not quite as straight forward a topic. We'll have to cover it later.