The Great Big Guide to Paper Circuits
Contributors:
Gella
Gella 
Creating Traces: Overview
A trace is a path that takes the place of wiring, most commonly seen on a printed circuit board. In paper circuits we'll use conductive materials as a substitute for wires on the paper's surface to connect components. In this tutorial we'll discuss three types of traces: paint, tape, and ink.
The green lines on this PCB are the traces connecting parts of the board.