hot spot: n. 1. [primarily used by C/UNIX programmers,

: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.
-- The AI Hackers Dictionary