The Collaborative International Dictionary of English v.0.48:

Tracing \Tra"cing\, n.
   1. The act of one who traces; especially, the act of copying
      by marking on thin paper, or other transparent substance,
      the lines of a pattern placed beneath; also, the copy thus
      producted.
      [1913 Webster]

   2. A regular path or track; a course.
      [1913 Webster]

   Tracing cloth, Tracing paper, specially prepared
      transparent cloth or paper, which enables a drawing or
      print to be clearly seen through it, and so allows the use
      of a pen or pencil to produce a facsimile by following the
      lines of the original placed beneath.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tracing paper
    n 1: a semitransparent paper that is used for tracing drawings