Definition: The term "broken in" is primarily used as an adjective to describe something, especially a horse, that has been tamed or trained to obey commands. When a horse is "broken in," it means that it is used to being ridden and is comfortable responding to the rider's instructions.
In a more general sense, "broken in" can describe something that has been made suitable for use through a process of adjustment or practice.
"Break in": To wear something until it becomes comfortable.
"Break someone in": To train someone for a new job or task.
"Broken in" is a useful term to describe the process of making something or someone ready for use through training or adjustment.