Also termed stock cycle, an inventory cycle is the fluctuation of GDP caused by the accumulation and the selling of stocks/inventories. If production is greater than demand, GDP will rise but companies will also accumulate unsold stocks. This will encourage some to scale back production, cutting GDP even if demand remains constant. An economic cycle is created and normally the inventory cycle amplifies the existing economic cycle as stocks are accumulated in good times and production is reduced in bad times.
In the global recession of 2008, demand plunged, leaving companies with significant unsold inventory. They responded by mothballing factories leading to a plunge in industrial production, output and GDP. Once the stock was sold output rose again purely because some production lines were restarted.