Impulse control is a dog's ability to pause before acting on a strong urge, whether that's the urge to grab food, chase something moving, or barrel through a doorway. It's less about a single trained behaviour and more about a general skill that gets stronger with practice, similar to a muscle.
Dogs aren't born with much impulse control. Puppies in particular tend to act on instinct first and think, if at all, second. Building this skill is one of the more valuable long-term investments an owner can make.