"A synthetic long stock position is where you emulate the potential outcomes of actually owning stock using options. To create one, you would buy at the money calls based on the relevant stock and then write at the money puts based on the same stock.
The price that you pay for the calls would be recouped by the money you receive for writing puts, meaning that if the stock failed to move in price you would neither lose nor gain: the same as owning stock. If the stock increased in price, then you would profit from your calls, but if it decreased in price, then you would lose from the puts you wrote. The potential profits and the potential losses are essentially the same as with actually owning the stock."
The biggest benefit here is the leverage involved; the initial capital requirements for creating the synthetic position are less than for buying the corresponding stock.
"Synthetic positions" are over advertised to be sure...definitely better for the brokerage houses more commish...