In a theological context, the grace which a sinner receives at the moment of their death. It is bestowed upon them by whatever higher power you perfer, an angel, Jesus, maybe God himself. This kind of grace, however, doesn't beeline you straight to Paradise. If you listen to Dante, you'll probably end up in Purgatory where you have to climb a very large hill in order to be cleansed of your sins before you are ready for the kingdom of heaven.

But rejoice not, last minute shoppers! This isn't a free ride final hour if-I'm-wrong-I'll-repent-on-my-deathbed ticket into the afterlife. You have to earn your grace through spontaneous conversion or profound belief in God at the last moment of your life. This theme was stated rather well by the recent movie Way of the Gun, which I paraphrase:

"What if, in those last moments of your life, you found God. What would you say in your defense?"

Well, if you have enough final conviction, then you don't need a defense, just some good walking boots for the ascent up that hill.