It's just a scar where another stem was broken off. The cambium will roll over it soon and you'll be unable to see it. You can hasten the process by carving it smooth or slightly indented so the living cambium is exposed all around the perimeter of the scar and carefully painting the freshly carved area with a thin coating of waterproof wood glue to prevent additional drying and die-back of the cambium surrounding the wound. Some people use Vaseline or even Preparation-H (Pauline Muth).

Al

what you said makes a lot of sense.
i've seen trees undergone that process you've said but without human intervention. (though i'm always doubtful and in need of someone who could verify that it does work)
ty