adverd

On or in a vehicle: This is the most common usage of "aboard" as an adverb. It refers to being physically present inside a means of transportation, such as a ship, airplane, train, bus, or car.

On base (baseball): In baseball, "aboard" is used to indicate that runners are on one or more bases.

Example

1. We were all aboard the ship when it finally set sail.
2. The flight attendant welcomed us aboard the airplane with a warm smile.
3. With two runners aboard, the batter hit a home run, scoring three runs.