A more thorough explanation:

Definition: Lex commercii refers to the law of business or commerce, also known as commercial law. It is a set of legal rules that governs business transactions and relationships between parties engaged in commerce.

Example: In Roman law, lex commissoria was a clause in a contract of sale that allowed the seller to cancel the sale if the buyer did not pay the agreed price by the specified time. This clause was also used in pledge agreements, where the debtor and creditor could agree that if the debtor failed to pay the debt on time, the creditor would obtain absolute title of the pledged property.

Explanation: The example illustrates how lex commissoria was used in Roman law to protect the interests of sellers and creditors in business transactions. It allowed them to cancel the sale or obtain ownership of the pledged property if the other party failed to fulfill their obligations. This clause was important in ensuring that business transactions were conducted fairly and efficiently.