This is the 16723rd most frequent Russian word.
скоростного
"Скоростного" means "high-speed" in English.
Here, 'скоростного' is used as an adjective modifying 'поезда' (train) to indicate that the train has high speed.
Мы проехали больше двух часов на скоростного поезда.
We traveled for more than two hours on a high-speed train.
In this sentence, 'скоростного' modifies 'шоссе' (highway) to describe its high-speed nature.
Постройка скоростного шоссе значительно улучшила транспортное сообщение.
The construction of the high-speed highway significantly improved transportation.
Here, 'скоростное' is describing 'интернет-соединение' (internet connection) to emphasize the speed of the connection.