Explain the Skip List data structure and its probabilistic properties.

A Skip List is a probabilistic data structure using multiple layers of sorted linked lists for O(log n) average search, insert, and delete. Each element has a random height (usually geometric distribution with p=0.5). Higher layers act as express lanes, enabling binary search-like behavior without rebalancing. Space is O(n) expected. Skip lists are simpler to implement than balanced trees and used in Redis sorted sets and LevelDB.