Answer in one word.
The innermost part of the Earth.

Explanation

**Step-by-Step Solution:**

1. **Understanding Earth's Structure**: The Earth is composed of several layers. The outermost layer is called the crust, followed by the mantle, and then the core.

2. **Identifying the Core**: The core is divided into two parts: the outer core and the inner core.

3. **Determining the Innermost Part**: Among these layers, the innermost part of the Earth is the inner core.

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