Final answer:
A hairline fracture is known as a nondisplaced fracture, which is a minor crack or bruise within the bone that remains in its original position.
Step-by-step explanation:
A hairline fracture is also known as a nondisplaced fracture. This type of fracture refers to a small crack or severe bruise within the bone. It's a term often used to describe a thin fracture that has occurred in the bone. Such fractures might not be easily visible on X-rays and do not involve the bone being displaced from its original position. Common types of fractures besides nondisplaced include transverse, oblique, spiral, comminuted, impacted, greenstick, open (or compound), and closed (or simple). The healing process for fractures typically begins with the formation of a hematoma, followed by callus formation, osteoclastic resorption, and osteoblastic bone formation, leading to bone remodeling.