Sorry, but I don know a correct keyword regarding this thing to find the answer myself.
It looks like a cage tool but it is not. It appears once an object is selected.
I don’t think that’s standard (I have never seen it). Do you have any custom plug-ins installed?
Thank you. Yes I have some plugins and all were installed a year ago but this thing appeared 2 days ago. What is interesting it is disappeared now - I did nothing in settings. I’ll let you know as soon as I see it again… 
I suspect ClippingBox maybe…
Ah, good to know, never knew about that option…