Fermillion

The fermillion is equal to $$10^{3 \cdot 10^{3 \cdot 10^{3 \cdot \text{quintillion}}} + 3}$$, or $$10^{3 \cdot 10^{3 \cdot 10^{3 \cdot 10^{18}}} + 3}$$. The term was coined by Jonathan Bowers.

Etymology
The name of this number is based on the word "Earth" (for "terra firm a") and the suffix "-illion".