A "sketch" is quick small strokes with a pen or pencil
a "contour" drawing is using long continuous lines and basically creating the outline of an image
both are great ways to draw
with the sketch you can feel and form the shapes of your object whereas with the contour drawing you see and draw your outlines which creates a more organic and less accurate line.
They each have their own personalities and flavor!
I prefer a micron .005 pen when I do a contour drawing.
What's your favorite?
and what do you like to draw with?