hot spot

hot spot 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.  See {tune}, {bum}, {hand-hacking}.  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. A screen region that is sensitive to mouse clicks, which trigger
   some action.  Hypertext help screens are an example, in which a hot
   spot exists in the vicinity of any word for which additional
   material is available.  4. 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).  5. More generally, any place
   in a hardware design that turns into a performance bottleneck due
   to resource contention.