The term knothole is used to refer to a block of stacked characters in a text that occurs when you have the same words or phrases repeated several times and the text is laid out in such a way that the words or phrases line up.
This is apparently quite a frequent occurrence in encyclopedias, which tend to have a house style for entries, which leads to quite a lot of repetition, and also in publications that use fairly narrow columns, such as newspapers and magazines.
Here’s an example:
Those concerned with page layout are trained to avoid such undesirable alignments of text.
Found via David Crystal’s blog.
