Astillion

The astillion is equal to $$10^{3 \times 10^{3 \times 10^{3 \times \text{trillion}}} + 3}$$, or $$10^{3 \times 10^{3 \times 10^{3 \times 10^{12}}} + 3}$$. The term was coined by Jonathan Bowers.

Etymology
The name of this number is based on the word "ast eroid" and the suffix "-illion".