The word train has several meanings:

1. A connected line of railroad cars pulled by an engine along tracks. Trains carry passengers and cargo across long distances. Before airplanes became common, trains were the fastest way to travel across countries.
2. To teach someone a skill through practice and instruction. Athletes train for competitions by practicing daily and building their strength. A new employee might train for several weeks to learn their job. When you train your dog to sit or stay, you're teaching it to respond to commands. Training requires patience and repetition: you get better at something by doing it over and over with guidance.
3. The long part of a formal gown that trails along the ground behind the person wearing it. A bride's wedding dress might have a train several feet long. At royal weddings, the train can stretch for many yards, requiring attendants to carry it.

The word can also describe a connected series of thoughts or events, like a train of thought (a sequence of connected ideas) or a train of events (things happening one after another in a logical sequence).