The word sic means 'so' or 'thus' in Latin. It is useful in academic writing for two things. First, used after a quotation, or (in [square brackets]) after an error inside a quotation, it indicates that the writer who is quoting it knows that the quotation contains an error. It says 'This is how the quotation that I used was written; so please do not think that I have made an error myself'. (This has an additional advantage that it may communicate to the reader 'Look! My own knowledge is good enough to have seen the error in the source'.)
The second use of sic is most useful in transcribing spoken material, reporting on face-to-face interviews and so on. It means 'This is what my source said. I know it sounds unlikely, or it is possible that he said something different from what he actually means; but these are the exact words he used'.
- Use the word sic in italic font. This shows that it is a foreign word - in this case Latin, the language of ancient Rome and medieval scholarship.