Introduction:
A hill is a landform that rises above the surrounding terrain and has a distinct peak or summit. It is characterized by its height and steepness, distinguishing it from other types of landforms such as plains or valleys. While hills can have various features like trees, animals, and water, the defining characteristic of a hill is its elevation or height.

Main Body:

1. Definition of a hill:
A hill is a natural landform that is typically higher than the surrounding land. It is formed through various geological processes such as tectonic activity, erosion, or volcanic activity. Hills can vary in size, shape, and composition, but their distinguishing feature is their height.

2. Height as the defining characteristic:
The primary characteristic that sets a hill apart from other landforms is its height. Unlike a plain or a valley, which are relatively flat or low-lying, a hill rises above the surrounding landscape. The height of a hill is subjective and can vary depending on the geographical context. However, it is generally understood that a hill is smaller in height compared to a mountain.

3. Relationship between hills and trees, animals, and water:
While hills can have trees, animals, and water, these features are not exclusive to hills. They can be found in various other types of landforms as well. Trees grow on hillsides and provide habitat for animals, while water sources like rivers or streams can flow through or around hills. However, these features do not define a hill as they are not unique to this landform.

4. Importance of hills:
Hills play a significant role in shaping the landscape and have various ecological, social, and economic importance. They provide habitat for diverse plant and animal species and contribute to biodiversity. Hills also serve as natural barriers, protecting lower-lying areas from erosion and floods. Additionally, they offer recreational opportunities like hiking, mountaineering, and sightseeing, attracting tourists and generating revenue for local communities.

Conclusion:
In conclusion, while a hill can have trees, animals, and water, the defining characteristic of a hill is its height or elevation. Hills rise above the surrounding landscape and are smaller in size compared to mountains. They play a crucial role in shaping the environment, providing habitat for wildlife, and offering recreational opportunities.