The Earth's core doesn't have a single, widely-used nickname. It's usually just referred to as "the core" or "Earth's core".

However, there are some less common terms that you might encounter:

* Geosphere: This term can refer to the Earth's entire solid body, but it's sometimes used specifically for the core.

* Inner and Outer Core: These are the two distinct layers of the Earth's core, but they are not considered nicknames.

Let me know if you have any other questions about the Earth's core!