a person or other animal having powers of endurance or perseverance; "the horse that won the race is a good stayer"

A horse which has the endurance to race well over long distances. Sometimes a person will comment that a horse can 'stay all day'. This means the horse in question is a good stayer and will continue to race at a said pace for however long is asked of them.

A runner that has the endurance to race well over long distances.

A horse which excels over longer distances

A horse that can run well at longer distances.