In my answer to the question about the opposite for bug in programming, I referred to 'bug' as a slang word.
Shaun Wilson, in his comment insists on 'bug' being a term that derived from a historical process:
"bug" is not "slang for error", "bug" is a historical term derived
from the process of fixing old vacuum tube based computers from
yesteryear, where a moth or similar would find its way into the
computer causing a short (and an error in programming). Thus the term
"debugging" was born, and still, today, we refer to programming errors
as "bugs". Often users refer to things as bugs which are not, such as
feature changes, or unexpected behaviors which are not bugs (but were
otherwise unintended.) This is also why we have a running joke about
certain bugs being features
While the above is a great note on the etymology, I still do not agree 'bug' is a term if used in computer programming; the term is something that is singular in meaning, singularity is a property of a term. Something other than one official term may be slang. In case of a live bug in vacuum tube it was the term describing the object literally. In case of computer bug, error is implied, and 'bug' is a figurative description.
So the question is: if a word used to be a term because it described an object literally (real bug), now is used figuratively (computer error), does it remain a term or is it a slang word?
Best Answer
The story of the real-life moth as a computer "bug" is told at length under the title "First Computer Bug." Even in this case, though, the way the people involved treated the incident suggests that the word bug was already understood metaphorically:
In fact, an instance where bug is used in the sense of "system problem" appears five years earlier than that, in The Autocar: A Journal Published in the Interests of the Mechanically Propelled Road Carriage, volume 87 (1942) [combined snippets]:
Another early use of bug in this metaphorical sense is from United States Investor, volume 61 (1950):
In both of the preceding examples the buggy system was political or economic. But in answer to an EL&U question (Origin of "bug" in reference to software) posed back in September 2011, researcher extraordinaire Hugo noted that bugs is used in a logbook entry from April 17, 1944, at Harvard’s Computation Laboratory (as reported by Peggy Kidwell in an article published in IEEE Annals of the History of Computing (December–October 1998)) in the specific context of computer operation, three years before the much-discussed moth episode:
Oxford Dictionaries online finds a much earlier instance of bug—this time in connection with the new technology of audio recording. From "Was the first computer 'bug' a real insect?":
The upshot is that bug was in use as a metaphorical or figurative term for a systemic problem in 1889. Whether that makes it a slang term more than a hundred years later is a matter of opinion, I suppose—but the notion that prior to the first figurative use of "computer bug," a bug was strictly and literally an insect appears to be incorrect in any case.