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What is that box!?

Hello!
Can someone please tell me what that lightly outlined box is? It’s not a bounding box for text wraparounds… I’ve checked that.
The lightly outlined box stays the same size when I resize the greenbox. It also disappears when I use the scale tool. The other way to get rid of it is to just re-draw the box altogether.
I would like to know what it is a how to properly get rid of it in case I see it again down the road. Knowing what it is can be beneficial.
Thanks in advance!
A.