I would clarify a template as being a shape made of fabric, paper, card stock, acrylic etc, and used to draw/cut/sew around - which can be used for applique, English paper piecing, quilting and arts in general.
Rulers are mainly straight sided with measurements marked, can be narrow, wide, square or oblong - though for longarm quilting machines they come in many shapes, but I would still class anything not straight sided as a template.
This is just the way I see things