It's about answering shortest path queries on (real) road networks in log n time, with an O(n) time and O(n) space preprocessing, where n is the number of nodes. These three bounds have not been simultaneously attained so far.
The constants are such that for the road map of Germany (about 4 million nodes) query times are below 1 millisecond, and preprocessing takes a couple of hours using about 2 GB of main memory of a standard PC. In comparison, a standard Dijkstra computation for this map takes a couple of seconds.