Could someone please help me out with this sentence. Whilst I understand the first part, I don't understand the last part in bold.
"The Fréchet distribution ($\xi > 0$) has a heavy tail with $1 − G_\xi (x) \sim ( \xi x) ^ {−1/ \xi}$ as $x \to \infty$, and, hence, moments only exist for order less than $1 / \xi $."
Particularly, what does "order less than $1 / \xi$" mean?