Mysterious White Box - Cue Points

I'm just learning, and somehow created a mysterious "white box" on my screen (see attachment). It does not appear in story view - only when I'm in a slide. I cannot delete it or minimize it except I can grab the edge and make it smaller. If I right click on the white area I can select "Create cue point at playhead" or Delete all cue points. Anyone know what I did or how to correct?

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