A security interest is said to be 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.
when the secured party has a legally enforceable right to take that property and sell it to satisfy the debt.
when the buyer takes the property subject to a mortgage and the seller agrees to continue paying the debt.
when the goods are sold but regained as soon as the debtor takes possession of the new property.