Final answer:
An incomplete fracture of the humerus indicates a partial break in the bone, such as a crack or bend but not a full separation, which is best described as 'a fracture that bends or splinters part of the bone'.
Step-by-step explanation:
An incomplete fracture of the humerus means that the bone has not been broken all the way through; it could be cracked or bent. Among the explanations provided, the most accurate description of an incomplete fracture is 'a fracture that bends or splinters part of the bone'. This can be contrasted with a complete fracture, where the bone is broken all the way through, and open fractures where the bone breaks through the skin. It's important for fractures to be managed properly to ensure that the bone heals in the correct anatomical position to prevent long-term deformities.