Search for the definition you are looking for.
To buy/sell mispriced options and hedge the market risk using only options, unlike the conversion or the reversal, which use futures contracts. If a certain strike put is underpriced, the trader buys the put and sells a call at the same strike, creating a synthetic short futures position. To get rid of the market risk, the trader sells another put and buys another call, but at different strike prices.
* see also conversion; reversal