This is no ordinary experiment. He sits a kid in front of a plate with one marshmallow. The kid is told that if he can wait 15 minutes without eating it, the kid will get 2 marshmallows.
Instant gratification is the desire to experience pleasure and fulfillment without delay. This is all about pleasure.
The children that delayed the gratification had higher SAT scores, lower substance abuse, dealt with stress better, and had better social skills.
Saving is delaying gratification. It is the part about not spending all of your money as quickly as you get it.