What is the meaning of Tetration?

The arithmetic operator consisting of repeated exponentiation, by analogy with exponentiation being repeated multiplication and multiplication being repeated addition, ${\displaystyle ^{b}a}$ denoting ${\displaystyle a}$ to the power of ${\displaystyle a}$ to the power of ${\displaystyle \ldots }$ to the power of ${\displaystyle a}$, in which ${\displaystyle a}$ appears ${\displaystyle b}$ times.

Source: wiktionary.org