This is the 1703rd most frequent Russian word.
борту
"Борту" means "to the board" or "to the side of a vessel/plane" (dative case of "борт").
Here, 'борту' refers to being physically on the board of a vehicle, such as a ship or an airplane.
Пассажиры уже находятся на борту.
The passengers are already on board.
In this context, 'борту' indicates the presence of crew members on the ship.
Экипаж на борту корабля подготовился к отплытию.
The crew on board the ship prepared for departure.
Here, 'борту' is used to describe location within an airplane.