Copying your saved game file to another directory, to circumvent auto-deletion. This is usually done in RPGs like Rogue that automatically delete the file as a form of "perma-death" so that you are required to start over every time you die.
"I used savescumming to get to the Amulet of Yendor just to prove to myself that it was possible. Someday I'll beat it for real."
In video games: Manually saving your game over and over again (usually before important decisions/boss battles, etc.) to make sure that if you screw up later on, you can always just return to your most recent savedgame.
Used in games that allow players to save whenever they want, thus making the game substantially easier because there's no real penalty for messing up, and it lets the player know what to expect ahead.
If I wasn't save scumming so much, I would've had to restart this mission a shitton of times.