Overset text occurs when a text box is too small for the type contained in it. This results in missing words, paragraphs or entire pages in a document. Though InDesign shows this both in Story Editor and the normal layout view, it is still easy to miss and can produce disastrous results. The fix is simple, and is literally nothing more than a couple of clicks of your mouse.
Find the overset text. If working in Story Editor, you can tell which text is overset by the red line running down the left side. All the text highlighted by that line is overset. If looking at a document in regular layout view, overset text is denoted by a small red box with a plus sign in it at the bottom right corner of a text box.
Change the box or the text to allow the type to fit. Changing the point size, deleting words or making the text box larger will get rid of the problem. If you change the size of the text box, the layout of the entire page may need to adjustment.
Check the document to be sure all the overset text is gone. Printing the document or exporting to PDF is the best way, as any overset text will cause an error message when trying to perform either of these operations.