Rendering is an arbitrary set of techniques, methods, and strategies (bag of tricks) oriented towards defining and interpreting the texture, form, and light phenomena of a given subject via surface (e.g. paper, canvas) and medium (e.g. pencil, ink, paint, etc.).
Drawing is essentially contour using line. The minute you start modifying the drawing by shading/coloring (additive rendering) or erasing away (subtractive rendering) the drawing phase ceases, and the rendering phase begins. Preserving the energy of the initial phases is oftentimes a signifier of an experienced painter, though attention to detail is just as valued if not more so.