The simple version would be "finger crawling", like you're dragging a piece of paper. I think it is intuitive, it just seems to need more explicit instruction for people nowadays who never really did arts and crafts as kids, and built their understanding on new non-physical conventions instead (like three-finger gestures as in the other reply - I find those weird, not at all intuitive, and sometimes difficult to do because my fingers are different lengths - drag is mostly fine since I can just move my whole hand, but other gestures not so much).