Brinelling  is the permanent indentation of a hard surface. It is named after the Brinell scale of hardness, in which a small ball is pushed against a hard surface at a preset level of force, and the depth and diameter of the mark indicates the Brinell hardness of the surface. Brinelling is permanent plastic deformation of a surface, and usually occurs while two surfaces in contact are stationary (such as rolling elements and the raceway of a bearings) and the material yield strength has been exceeded. 
Brinelling is undesirable, as the parts often mate with other parts in very close proximity.  The very small indentations can quickly lead to improper operation, such as chattering or excess vibration, which in turn can accelerate other forms of wear, such as spalling and ultimately, failure of the bearing.