Final answer:
The flared portion of a long bone between the diaphysis and the epiphyseal plate is known as the metaphysis.
Step-by-step explanation:
The flared portion of a long bone between the diaphysis and the epiphyseal plate is called the metaphysis. The metaphysis serves as the narrow area containing the epiphyseal plate, which is crucial for the lengthwise growth of long bones during development. Once a person reaches early adulthood, the cartilage within the epiphyseal plate is replaced by osseous tissue, and the epiphyseal plate becomes known as the epiphyseal line.