Professor wants clean pages, what is pdf annotations when printing?

My professor said my printed term paper needs to be completely clean, but my print dialog has an option for PDF annotations. What actually counts as an annotation when printing out a document?

I ran into this when printing client contracts: annotations usually mean added comments, highlights, sticky notes, drawings, stamps, or other markup, not the original text. Leave “PDF annotations” unchecked, then check the print preview to make sure no comments or highlights appear on the pages.