Sentence:  <WSD>Metaknowledge</WSD> is knowledge about knowledge ... The hallmark of <WSD>metaknowledge</WSD> is its being a matter of knowing propositions in which one "K"[nowledge]-operator occurs within the scope of another. Knowledge about someone's ignorance thus counts as <WSD>metaknowledge</WSD>. 
Meaning of the word marked with <WSD> tags:  Knowledge about knowledge itself.