Final answer:
An open fracture occurs when a broken bone breaks the skin or a wound reaches the fracture site, posing a higher infection risk.
Step-by-step explanation:
When a fragment of a fractured bone breaks the skin, or when a wound extends to the site of the fracture, it is known as an open fracture. An open fracture, also referred to as a compound fracture, carries a high risk of infection due to the exposure of the bone and internal tissues to the environment. This is in contrast to a closed fracture, where the skin remains intact over the break.