Drawing

Patent drawings must show every feature of the invention as specified in the claims. Omission of drawings may cause an application to be considered incomplete but are only required if drawings are necessary for the understanding of the subject matter sought to be patented.

-- see Drawing Requirements for more info

A figure filed as part of a patent application to describe and explain an invention. At some point in the proceedings, the drawings must comply with the patent office requirements for formal drawings. MPEP 608.02, MPEP 608.02(a), MPEP 608.02(b).