n. 1. [primarily used by C/UNIX programmers, but spreading] It is received wisdom that in most programs, less than 10% of the code eats 90% of the execution time; if one were to graph instruction visits versus code addresses, one would typically see a few huge spikes amidst a lot of low-level noise. Such spikes are called 'hot spots' and are good candidates for heavy optimization or hand-hacking. The term is especially used of tight loops and recursions in the code's central algorithm, as opposed to (say) initial set-up costs or large but infrequent I/O operations.
2. The active location of a cursor on a bit-map display.
"Put the mouse's hot spot on the 'ON' widget and click the left button."
3. In a massively parallel computer with shared memory, the one location that all 10,000 processors are trying to read or write at once (perhaps because they are all doing a busy-wait on the same lock).