Silly Question

[DLDTEX]

Howdy I am new to the forum and new to Madbean projects.  The on-line docs have a layout of the components on a PCB.  The red line on the layout is a little confusing.  What exactly does the red line represent?

Sign embarrassed

[tenwatt]

Most of the boards are doublesided.  They have traces on the front and back.  I believe the red lines are just the traces on the back.