A more thorough explanation:

Definition: Per aes et libram is a Latin term used in Roman law that means "by bronze (or copper) and scales." It refers to a fictitious sale in a mancipation where the purchaser strikes the scales with a piece of bronze or copper and gives it to the seller as a symbol of the price.

Mancipation is a legal formality for transferring property by either an actual or a simulated purchase. It is a formal conveyance in the guise of a sale. The formality required the presence of the thing being conveyed (res mancipi), and of five adult male citizens acting as witnesses. Another person (the purchaser) would strike the scales with a piece of bronze or copper and give it to the seller as a symbol of the price.

For example, if someone wanted to transfer ownership of a piece of land to another person, they would go through the mancipation process. The purchaser would strike the scales with a piece of bronze or copper and give it to the seller as a symbol of the price. This would signify the transfer of ownership from the seller to the purchaser.

Overall, per aes et libram and mancipation were important legal processes in ancient Rome for transferring ownership of property.