The term "train" has several meanings, depending on its context.
1) In a general sense, train refers to a group or series of connected vehicles that move together along a guide rail or track. This is commonly used in reference to public transportation systems such as subways and trains.
2) Train can also refer to the act of training or teaching someone something through practice and repetition. For example, "I'm going to start training for my marathon."
3) In a more specific sense, train refers to a type of animal that is typically kept as a pet or used for work such as pulling carts or plowing fields. Examples include horses, dogs and even bears in some cultures!