: a thickening of or a hard thickened area on skin
: a mass of exudate and connective tissue that forms around a break in a bone and is converted into bone in the healing of the break
In botany, soft tissue that forms over a wounded or cut plant surface, leading to healing. A callus arises from cells of the cambium. When a callus forms, some of its cells may organize into growing points, some of which in turn give rise to roots while others produce stems and leaves. Thus a callus may be capable of regenerating an entire plant.