what does $O(\alpha(n))$ amortized time mean?

DELETE(S, i): Delete integer $ i$ from the set $ S$ . if $ i \notin S$ , there is no effect.

from a set of consectutive integers like $ S = \{1,2,3,5,6\}$

Provide a data structure and an algorithm for DELETE that takes $ O(\alpha(n))$ amortized time


not sure what what does $ O(\alpha(n))$ amortized time mean?

I was thinking AVL trees ? I know the worst case is $ O(log(n))$ for that. Not sure what $ O(\alpha(n))$ amortized time means though.