UV scrolling
Moving a texture's UV coordinates over time so the surface appears to move, while nothing in the geometry actually does.
The cheapest animation in real-time graphics moves no geometry at all. By adding time × speed to the UV coordinates in a material's shader, the texture slides across the surface: a waterfall runs, a conveyor belt rolls, a force field pulses. Because the texture tiles seamlessly, no end and no extra data are needed — just one scalar per frame.
The trick scales up with several layers scrolling at different rates to hide the repetition, and is often combined with a flow map that steers direction per pixel for swirling water or lava. The limitation is that the motion is purely visual: a UV-scrolled river will not carry a floating boat. That needs real simulation.