This is the 312th most frequent French word.
train
A railway vehicle for transporting passengers or goods.
Here, 'train' refers to a mode of transportation, specifically a railway vehicle.
Le train arrive à la gare.
The train arrives at the station.
Here, 'en bon train' is an idiomatic expression meaning that something is advancing or making progress effectively.
Le projet est en bon train.
The project is progressing well.
In this context, the phrase 'en train de' is used to indicate an ongoing action and 'train' functions as part of this fixed expression.