Tracing Paper, is simply a semi-transparent paper than enable you to trace an underlying image,

Tracing paper is used for easier tracing and transfer most commonly as a step in another fine art process. In this way tracing paper is used to temporarily record the traced image and then with the aid of carbon paper laid underneath, the image is retraced once again and thus transfered to another surface.

Tracing Paper is often used to transfer images & designs in printmaking for example, tracing paper may also be used along with a light box.