I like the way that Miles Wilson, a faculty member in the MFA program in creative writing at Texas State University, once described the nature of a short story. I heard him give a speech on the topic several years ago.
He said that a short story presents a slice of life in which something dramatic happens to the main character, after which he’s never the same. His circumstances might not have changed, but his way of seeing them or himself is different.
Jan Kilby, Writing Consultant 