The mirror of synthetic-long-stock. Delta is about −1.00, and the position profits dollar-for-dollar as the underlying falls.
Its real use is avoiding the stock loan market. Shorting a hard-to-borrow name can cost 30% a year in borrow fees, or be impossible because no locate exists. The synthetic needs no borrow — though the options will already price in that cost, which is exactly why the put looks expensive relative to the call.
Example: XYZ at $50 with a 20% annual borrow rate. Sell the $50 call for $2.30, buy the $50 put for $4.40, net credit −$2.10. The $2.10 you effectively pay over parity is the market charging you roughly the same borrow cost the stock loan desk would.
Related: synthetic-long-stock, hard-to-borrow, put-call-parity, reversal-arbitrage