A small movement at the handle of a bullwhip produces an enormous (and oscillating) movement further down the the whip, it's an analogy for movements in customer demand having large effects further down the supply chain.

See first illustration: http://enwp.org/Bullwhip_effect The graph representing over-/undersupply resembles the movements of a whip.

Out of curiosity: did you try to look up the answer to your question before asking it here?