Which of the following best describes a "hemisphere"?

A hemisphere refers to half of the Earth, which can be divided in various ways, most commonly by the equator or the prime meridian. When the Earth is divided by the equator, it creates the Northern and Southern Hemispheres, while dividing it by the prime meridian creates the Eastern and Western Hemispheres. This division is fundamental in geography as it helps in understanding global geography, climate patterns, and time zones.

The other options, while related to geography, do not accurately define what a hemisphere is. Climate zones, cultural identities, and geographic areas defined by elevation are classifications that focus on different aspects of geography rather than splitting the Earth into two distinct halves. Therefore, the correct answer captures the essence of the term "hemisphere" effectively by highlighting its role in dividing the Earth into two equal parts.