"I don't know" is an expression of unknowingness, lack of knowledge and something else which is not known at the moment. It has the abbreviations idk, IDK, and id'tk, and the colloquials dunno, idunno, don't know, eyedoonutnoe, know, I do not, such a fact cannot be correctly perceived at this time, or at all if such accuracy is required, aggunuh, hell, I don't know and ask again later.