Walk-off home run?

As South Florida's biggest athletic supporter, I love all of our sports teams. When I saw that the Marlins beat the Phillies with Dan Uggla's home run in the 9th, I was thrilled. However it was the terminology that had me perplexed; it was called a "walk-off grand slam". Grand slam I know, but walk-off? I found out it's a relatively new term that basically means a home run that ends the game. Since Philadelphia pilfered our first place spot, I couldn't be more thrilled for Dan and the Marlins... Go Fish!