What is an aquifer?

Explanation

### Step-by-Step Solution:

1. **Definition of Aquifer**: An aquifer is defined as an underground layer of water-bearing rock or sediment that can store and transmit water. It is located below the water table.

2. **Location**: Aquifers are typically found beneath the ground surface, often composed of materials such as sand, gravel, clay, or rock.

3. **Water Storage**: These layers are porous, meaning they have spaces that can hold water. When rainwater or other sources of water seep into the ground, it can fill these spaces, creating a reservoir of water.

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