Print Area
You can define a rectangular area on the canvas, which is called the Print Area.  When printing, you can choose to print the area defined as Print Area.

The Print Area is indicated with a red rectangle on the screen, unless you have turned off the Print Area.

When you have configured the Print Area with a colored frame, then this frame will be shown instead of the red rectangle.

You can select the Print Area by clicking on the red line (or the frame).  When selected, you can resize and move the Print Area.