Blender 2.8 Beta - Unknown Rectangle when camera is selected I just started trying Blender 2.80 Beta. 

I noticed that there's this additional rectangle (image below) that I have no idea where did it come from. I can resize this rectangle but I don't know what is this rectangle for or what is this called. It does not seem to be related to the rendered image boundary, etc. It seems to be different from this yellow rectangle around the camera in 2.8 Beta  

Thanks a lot!
That is the Render Border. When rendered shading is active, the render will be constrained to that portion of the screen. You can disable it with CtrlAltB, or you can enable and/or draw a new one with CtrlB.

See Render Border&#39;s related check boxes - How do they work? for a more complete overview of its functionality.