What does the idiom, 'a slow coach' mean?

The idiom "a slow coach" means a lethargic fellow. This means that the person being referred to is someone who is slow, lazy, or lacks energy or enthusiasm. They may take a long time to complete tasks or move at a slower pace than others. So, if someone calls another person a "slow coach," they are saying that the person is generally slow and lacking in energy or motivation.