Well, here is the short and sweet description about smart contract & audit. Smart Contract is a virtual contract which is build from the existing blockchain and business people make use of it in a worthy way. When the contract is over the fund amount will be transmitted automatically to other person and if there is any change in the contract it will automatically notify to other person.
So it make the asset safe alongside other benefits. Smart Contract Audit is nothing but the advanced version of smart contract with all bug fixed and upgraded features.