I do not know what these are called, so googling them proved difficult. They appear wherever I move my mouse across the page and are very distracting, so I would like to turn them off. Who here can help solve this deceptively simple problem?
You have the Gap tool selected (fourth from the top on the Tools panel). Choose the Selection tool (black arrow, top tool).
It appeared to be a combination of the gap tool and an InDesign glitch. Even after switching to Selection tool, the gap boxes remained (as you can see in my screenshot). I had to quit the program and reopen the document before the gaps went away. All the same, thanks for letting me know.
Of course, that tool shouldn't shouldn't retain its appearance when you change tools.
You might try restoring your InDesign preferences. Here's how: