What is the meaning of the title in the short story "Story of an Hour"? And what idea or fact does Kate Chopin want to emphasize with this title?

To me, what the author is trying to emphasize by using this title is that Mrs. Mallard's whole life, in essence, is lived in the space of this one hour.  She goes through such major changes in her outlook, all in this very short time.

At the start of the hour, she is a "normal" housewife of the time.   She is devoted to her husband and shocked when she hears of his death.  But then she realizes that, for the first time in her life, she is free.  She lives a different life for the rest of that hour -- it is different from any mindset she has ever had before.  Finallly, she is brought back to reality and dies.

So I think that the emphasis is on these huge changes that occur in her mental and emotional state during this single hour.