Petotetrotos

Petotetrotos is equal to \(f_{\psi(I\uparrow\uparrow 10^{15})}(10)\) using the fast-growing hierarchy and the fundamental sequences for the functions collapsing weakly inaccessible cardinals. The term was coined by wiki user Denis Maksudov.

Etymology
The 4 parts of the name, "peto", "tetr", "ot" and "os", mean \(10^{15}\), tetration, the first inaccessible cardinal \(I_1\) and the function collapsing weakly inaccessible cardinals respectively, which form \(\psi(I\uparrow\uparrow 10^{15})\) when concatenated backwards. So the full name indicates the ordinal index of the number.