What is a Stencil?
Microsoft Definition: A collection of masters associated with a particular Microsoft Visio drawing type, or template. By default, stencils that open with a template are docked on the left side of the drawing window. You can open stencil (.vss) files independently of a template. Basically, a Stencil contains Shapes that are used to create a diagram. The Shapes can range from simple flow chart boxes or lines to more complicated Shapes like Servers, Racks or anything else that needs to be represented in a graphical form.