It is used as a reference for transactions using “P2SH” addresses as defined by BIP 016. A public key is provided by seller, market and vendor and is used to create an unique address which requires any of the two parties to sign in order to redeem. The most part is the “redeemScript” which contains the details of how to redeem the funds sent to the address, which is a hash of the redeemScript. The aim of the method is that no single party has enough knowledge to take funds away from these P2SH addresses. And it covers the terrible scenario of a market being shut down, the buyer and the seller with the redeemScript can finalize the transaction outside the market if both of them agree.