"Sic" is used after quotations that contain some kind of mistake to indicate that the preceding is what the source actually said, and not a typographical error.
This word is used most often in business, formal and technical writing. The word "sic" is placed in brackets, sometimes in italics, directly after the error in quotation. "Sic" can be used as a subtle way to make fun of the quoted source by pointing out the error. It can be used after a spelling error to indicate that the quoted source, and not the writer, made the error.
"Sic" comes from the Latin word meaning "thus," "so," "as such," or "in such a manner." It is pronounced to rhyme with "wick," though in the original Latin it would have rhymed with the English word "seek."
Latin was used as a universal academic language in Europe until the 18th century. Though Latin is a dead language in the 21st century, it's still important because of its history and influence on many modern languages. Many Latin abbreviations are still commonly used for their simplicity and precision, and because of Latin's status as a language of learned people.
A word in quotes with "sic" after it may mean two different things: that in the source, the word was in quotes, or that that particular word was used in the source. Some readers may be confused by these ambiguities. Using Latin phrases in your writing may cause you to sound too formal or even overbearing.