Final answer:
A security interest is perfected when the secured party has done everything as required by the law to establish their priority over others in relation to the collateral.
Step-by-step explanation:
A security interest is perfected when the secured party has done everything that the law requires to give the secured party greater rights to the goods than others have. It means that the secured party has complied with all legal requirements to establish their priority over other parties in relation to the collateral, which is something valuable that can be seized and sold if the buyer fails to repay the loan. Perfection of the security interest provides protection to the secured party in case of default or insolvency by the debtor.