What is an oasis?

An oasis is defined as a fertile area in a desert where water is available, allowing for the growth of vegetation and providing a habitat for various forms of life. The presence of water, often coming from underground aquifers that rise to the surface, distinguishes an oasis from the surrounding arid environment. This unique characteristic makes it a crucial resource for both wildlife and human populations, particularly in desert regions where access to water is otherwise limited.

The other options describe different concepts that do not encompass the definition of an oasis. For instance, while a region with abundant wildlife may sometimes overlap with the characteristics of an oasis, it does not specify the critical element of water availability or the desert setting. Similarly, a type of geological formation is not inherently tied to the idea of water and vegetation in a desert context. Lastly, an urban area with high population density pertains to human settlements rather than the natural features associated with oases. Thus, the most accurate and fitting description in this case is that of a fertile area in a desert with water and vegetation.