The answer to the crossword puzzle is TYPO, which stands for 'typographical error'. A typographical error is an unintentional mistake in the spelling, punctuation, or grammar of a written text. It is usually caused by a mistake in typing or printing, but can also be caused by a mistake in handwriting. Typographical errors can range from minor mistakes such as a missing letter or punctuation mark, to more serious errors such as incorrect words or sentences.