The word "improbability" means something that is unlikely or not very likely to happen. It refers to situations or events that have a low chance of occurring. Full definition
I do not understand why people wish to diminish the wonder of nature and the immense statistical improbability of our existence by giving credit to a powerful imaginary friend. (religion.blogs.cnn.com)
The fact that this is a massive statistical improbability did nothing to dent this conviction. (bookbrowse.com)
Natural selection can be seen as a kind of improbability drive that — given enough time — makes the apparently impossible extremely likely. (newscientist.com)