This is the 5893rd most frequent Russian word.
рейса
"Рейса" is the genitive singular or nominative plural form of "рейс," which means "flight," "voyage," or "trip" in English (usually referring to transportation).
Here, 'рейса' is in the genitive singular case, indicating an association with the flight that was missed.
Вчера я опоздал на рейс из Москвы в Санкт-Петербург.
Yesterday I missed the flight from Moscow to St. Petersburg.
In this usage, 'рейса' again is in the genitive singular case, because it relates to the arrival ('прибытие') of the flight.
Мы ожидали прибытие рейса в аэропорту.
We were awaiting the arrival of the flight at the airport.
Here, 'рейса' is in the genitive singular case, showing ownership or association with the cancellation ('отмена') event.