Incremental crop of a side via keyboard shortcut

I belive there is a keyboard shortcut (once stumbled across before, but now cannot refind)  for moving any one side of a frame over incrementally, with the option to do it in very fine increments, yes? To be clear, it's not scaling and it's not moving the entire image inside the frame. It's moving one side, thus cropping from that side, precisely, without dragging it manually via the mouse. Appreciatively...