Final answer:
A fourth-degree burn refers to a burn injury that damages not just the skin but also the deep tissues including fat, muscle, and bone, and it often requires significant medical intervention to heal.
Step-by-step explanation:
A fourth-degree burn is characterized by a burn injury to the deep levels of fat, muscle, or bone. This type of burn involves the full thickness of the skin and extends beyond, causing damage to the underlying muscle and even bone. Unlike burns that affect just the epidermis or epidermis and dermis, a fourth-degree burn damages the nerve endings to the point that the pain may not be as severe because the sensory function is compromised. However, full-thickness burns of this severity cannot heal on their own and often require medical interventions such as excision, skin grafts, or even amputation.