A stimulant is a drug that speeds up your body or an event that spurs you to action. Both types of stimulant get you going.
You might drink coffee in the morning for a reason: the caffeine in coffee is a stimulant, which gives you energy and helps you wake up. Other stimulants are much more harmful, such as illegal drugs like cocaine, but all stimulants speed up your system. Also, a stimulant can be anything that arouses action. When Pearl Harbor was attacked, it was a stimulant that drove America into World War II.