With respect to the cache, a "hot block" is any block that is intensively accessed and/or updated such that there is some contention for its buffer lock or for the cache buffers chains latch needed to locate it. (In general, any resource is said to be "hot" if the concurrency of access is sufficient to cause some contention or otherwise delay access to the resource.) The APT scripts actually look for the "hottest" resources, rather than just "hot" resources, and the heuristic that is used as the threshold is "twice the average" amount of contention.

I was looking at your scripts that address the buffer cache. What is a "hot block"?