What's that cyan box?

I’ve been using Blender for a couple of years now, but something’s appearing that’s got me stuck! One of my objects has gained an additional cyan dotted outline box, appearing some distance away from the object. If I select the object itself and go into edit mode, the box turns cyan, but I don’t seem to be able to do anything with the box itself. What is it, how did it get there, and how can I get rid of it? I can’t believe I’ve never seen this before after using Blender for so long :confused: . Picture attached.
Many thanks in advance…

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That looks like something that might appear if you have ghosting/all frames turned on while animating, but it is hard to tell from the image.

It looks like the object’s texture space. Is TexSpace turned on in the Object buttons->Draw panel?

Usually a cyan colored object means that it is linked in from another file.
The dashed cyan would be when you move the texture space away from the object.

Not sure how you got it into your current file unknowingly because it takes a few steps to do.

Also if you try to change it, usually you will see a “Can’t edit extern libata” error. (which you didn’t mention).

I don’t think it’s display keys, because those are displayed in yellow.

This is so that you can bring in data from other files and it’s “locked” so that you can only modify it in the original file that it came from or if you make it ‘local’ to the current blend file/scene by clicking the little Library icon in the Object and Links panel in the Object buttons window.